Darwiniana; Essays and Reviews Pertaining to Darwinism Part 13

The length of the a.n.a.lysis of the first book on our list precludes the notices which we intended to take of the three others. They are all the production of men who are both scientific and religious, one of them a celebrated divine and writer unusually versed in natural history. They all look upon theories of evolution either as in the way of being established or as not unlikely to prevail, and they confidently expect to lose thereby no solid ground for theism or religion. Mr. St. Clair, a new writer, in his "Darwinism and Design; or, Creation by Evolution," takes his ground in the following succinct statement of his preface:

"It is being a.s.sumed by our scientific guides that the design-argument has been driven out of the field by the doctrine of evolution. It seems to be thought by our theological teachers that the best defense of the faith is to deny evolution in toto, and denounce it as anti-Biblical. My volume endeavors to show that, if evolution be true, all is not lost; but, on the contrary, something is gained: the design-argument remains unshaken, and the wisdom and beneficence of G.o.d receive new ill.u.s.tration."

Of his closing remark, that, so far as he knows, the subject has never before been handled in the same way for the same purpose, we will only say that the handling strikes us as mainly sensible rather than as substantially novel. He traverses the whole ground of evolution, from that of the solar system to "the origin of moral species." He is clearly a theistic Darwinian without misgiving, and the arguments for that hypothesis and for its religious aspects obtain from him their most favorable presentation, while he combats the dysteleology of Hackel, Buchner, etc., not, however, with any remarkable strength.

Dr. Winch.e.l.l, chancellor of the new university at Syracuse, in his volume just issued upon the "Doctrine of Evolution," adopts it in the abstract as "clearly as the law of universal intelligence under which complex results are brought into existence" (whatever that may mean), accepts it practically for the inorganic world as a geologist should, hesitates as to the organic world, and sums up the arguments for the origin of species by diversification unfavorably for the Darwinians, regarding it mainly from the geological side. As some of our zoologists and palaeontologists may have somewhat to say upon this matter, we leave it for their consideration. We are tempted to develop a point which Dr. Winch.e.l.l incidentally refers to--viz., how very modern the idea of the independent creation and fixity of species is, and how well the old divines got on without it. Dr. Winch.e.l.l reminds us that St. Augustine and St. Thomas Aquinas were model evolutionists; and, where authority is deferred to, this should count for something.

Mr. Kingsley's eloquent and suggestive "Westminster Sermons," in which he touches here and there upon many of the topics which evolution brings up, has incorporated into the preface a paper which he read in 187i to a meeting of London clergy at Sion College, upon certain problems of natural theology as affected by modern theories in science. We may hereafter have occasion to refer to this volume. Meanwhile, perhaps we may usefully conclude this article with two or three short extracts from it:

"The G.o.d who satisfies our conscience ought more or less to satisfy our reason also. To teach that was Butler's mission; and he fulfilled it well.

But it is a mission which has to be refulfilled again and again, as human thought changes, and human science develops, For if, in any age or country, the G.o.d who seems to be revealed by Nature seems also different from the G.o.d who is revealed by the then-popular religion, then that G.o.d and the religion which tells of that G.o.d will gradually cease to be believed in.

"For the demands of reason--as none knew better than good Bishop Butler--must be and ought to be satisfied. And, therefore, when a popular war arises between the reason of any generation and its theology, then it behooves the ministers of religion to inquire, with all humility and G.o.dly fear, on whose side lies the fault; whether the theology which they expound is all that it should be, or whether the reason of those who impugn it is all that it should be."

p.r.o.nouncing it to be the duty of the naturalist to find out the how of things, and of the natural theologian to find out the why, Mr. Kingsley continues:

"But if it be said, 'After all, there is no why; the doctrine of evolution, by doing away with the theory of creation, does away with that of final causes,' let us answer boldly, 'Not in the least.' We might accept all that Mr. Darwin, all that Prof. Huxley, all that other most able men have so learnedly and acutely written on physical science, and yet preserve our natural theology on the same basis as that on which Butler and Paley left it. That we should have to develop it I do not deny.

"Let us rather look with calmness, and even with hope and good-will, on these new theories; they surely mark a tendency toward a more, not a less, Scriptural view of Nature.

"Of old it was said by Him, without whom nothing is made, 'My Father worketh hitherto, and I work.' Shall we quarrel with Science if she should show how these words are true? What, in one word, should we have to say but this: 'We know of old that G.o.d was so wise that he could make all things; but, behold, he is so much wiser than even that, that he can make all things make themselves?' "

CHARLES DARWIN: A SKETCH

(Nature, June 4, 1874, accompanying a portrait)

Two British naturalists, Robert Brown and Charles Darwin, have, more than any others, impressed their influence upon science in this nineteenth century. Unlike as these men and their works were and are, we may most readily subserve the present purpose in what we are called upon to say of the latter by briefly comparing and contrasting the two.

Robert Brown died sixteen years ago, full of years and scientific honors, and he seems to have finished, several years earlier, all the scientific work that he had undertaken. To the other, Charles Darwin, a fair number of productive years may yet remain, and are earnestly hoped for. Both enjoyed the great advantage of being all their lives long free from exacting professional duties or cares, and so were able in the main to apply themselves to research without distraction and according to their bent.

Both, at the beginning of their career, were attached to expeditions of exploration in the southern hemisphere, where they ama.s.sed rich stores of observation and materials, and probably struck out, while in the field, some of the best ideas which they subsequently developed. They worked in different fields and upon different methods; only in a single instance, so far as we know, have they handled the same topic; and in this the more penetrating insight of the younger naturalist into an interesting general problem may be appealed to in justification of a comparison which some will deem presumptuous. Be this as it may, there will probably be little dissent from the opinion that the characteristic trait common to the two is an unrivaled scientific sagacity. In this these two naturalists seem to us, each in his way, preeminent. There is a characteristic likeness, too--underlying much difference--in their admirable manner of dealing with facts closely, and at first hand, without the interposition of the formal laws, vague ideal conceptions, or "glittering generalities" which some philosophical naturalists make large use of.

A likeness may also be discerned in the way in which the work or contributions of predecessors and contemporaries are referred to. The brief historical summaries prefixed to many of Mr. Brown's papers are models of judicial conscientiousness. And Mr. Darwin's evident delight at discovering that some one else has "said his good things before him," or has been on the verge of uttering them, seemingly equals that of making the discovery himself. It reminds one of Goethe's insisting that his views in morphology must have been held before him and must be somewhere on record, so obvious did they appear to him.

Considering the quiet and retired lives led by both these men, and the prominent place they are likely to occupy in the history of science, the contrast between them as to contemporary and popular fame is very remarkable. While Mr. Brown was looked up to with the greatest reverence by all the learned botanists, he was scarcely heard of by any one else; and out of botany he was unknown to science except as the discoverer of the Brownian motion of minute particles, which discovery was promulgated in a privately-printed pamphlet that few have ever seen. Although Mr. Darwin had been for twenty years well and widely known for his "Naturalist's Journal,"

his works on "Coral Islands," on "Volcanic Islands, and especially for his researches on the Barnacles, it was not till about fifteen years ago that his name became popularly famous. Ever since no scientific name has been so widely spoken. Many others have had hypotheses or systems named after them, but no one else that we know of a department of bibliography. The nature of his latest researches accounts for most of the difference, but not for all, The Origin of Species is a fascinating topic, having interests and connections with every branch of science, natural and moral. The investigation of recondite affinities is very dry and special; its questions, processes, and results alike--although in part generally presentable in the shape of morphology--are mainly, like the higher mathematics, unintelligible except to those who make them a subject of serious study. They are especially so when presented in Mr. Brown's manner.

Perhaps no naturalist ever recorded the results of his investigations in fewer words and with greater precision than Robert Brown: certainly no one ever took more pains to state nothing beyond the precise point in question.

Indeed, we have sometimes fancied that he preferred to enwrap rather than to explain his meaning; to put it into such a form that, unless you follow Solomon's injunction and dig for the wisdom as for hid treasure, you may hardly apprehend it until you have found it all out for yourself, when you will have the satisfaction of perceiving that Mr. Brown not only knew all about it, but had put it upon record. Very different from this is the way in which Mr. Darwin takes his readers into his confidence, freely displays to them the sources of his information, and the working of his mind, and even shares with them all his doubts and misgivings, while in a clear exposition he sets forth the reasons which have guided him to his conclusions. These you may hesitate or decline to adopt, but you feel sure that they have been presented with perfect fairness; and if you think of arguments against them you may be confident that they have all been duly considered before.

The sagacity which characterizes these two naturalists is seen in their success in finding decisive instances, and their sure insight into the meaning of things. As an instance of the latter on Mr. Darwin's part, and a justification of our venture to compare him with the facile princeps botanicorum, we will, in conclusion, allude to the single instance in which they took the same subject in hand. In his papers on the organs and modes of fecundation in Orchideae and Asclepiadeae, Mr. Brown refers more than once to C.K. Sprengel's almost forgotten work, shows how the structure of the flowers in these orders largely requires the agency of insects for their fecundation, and is aware that "in Asclepiadeae . . . the insect so readily pa.s.ses from one corolla to another that it not unfrequently visits every flower of the umbel." He must also have contemplated the transport of pollen from plant to plant by wind and insects; and we know from another source that he looked upon Sprengel's ideas as far from fantastic. Yet, instead of taking the single forward step which now seems so obvious, he even hazarded the conjecture that the insect-forms of some orchideous flowers are intended to deter rather than to attract insects. And so the explanation of all these and other extraordinary structures, as well as of the arrangement of blossoms in general, and even the very meaning and need of s.e.xual propagation, were left to be supplied by Mr. Darwin. The aphorism "Nature abhors a vacuum" is a characteristic specimen of the science of the middle ages. The aphorism "Nature abhors close fertilization," and the demonstration of the principle, belong to our age, and to Mr. Darwin. To have originated this, and also the principle of natural selection--the truthfulness and importance of which are evident the moment it is apprehended--and to have applied these principles to the system of Nature in such a manner as to make, within a dozen years, a deeper impression upon natural history than has been made since Linnaeus, is ample t.i.tle for one man's fame.

There is no need of our giving any account or of estimating the importance of such works as the "Origin of Species by means of Natural Selection," the "Variation of Animals and Plants under Domestication," the "Descent of Man, and Selection in Relation to s.e.x," and the "Expression of the Emotions in Men and Animals"--a series to which we may hope other volumes may in due time be added. We would rather, if s.p.a.ce permitted, attempt an a.n.a.lysis of the less known, but not less masterly, subsidiary essays, upon the various arrangements for insuring cross-fertilization in flowers, for the climbing of plants, and the like. These, as we have heard, may before long be reprinted in a volume, and supplemented by some long-pending but still unfinished investigations upon the action of Dionaea and Drosera--a capital subject for Mr. Darwin's handling.

A propos to these papers, which furnish excellent ill.u.s.trations of it, let us recognize Darwin's great service to natural science in bringing back to it Teleology; so that, instead of Morphology versus Teleology, we shall have Morphology wedded to Teleology. To many, no doubt, evolutionary Teleology comes in such a questionable shape as to seem shorn of all its goodness; but they will think better of it in time, when their ideas become adjusted, and they see what an impetus the new doctrines have given to investigation. They are much mistaken who suppose that Darwinism is only of speculative importance, and perhaps transient interest. In its working applications it has proved to be a new power, eminently practical and fruitful.

And here, again, we are bound to note a striking contrast to Mr. Brown, greatly as we revere his memory. He did far less work than was justly to be expected from him. Mr. Darwin not only points out the road, but labors upon it indefatigably and unceasingly. A most commendable n.o.blesse oblige a.s.sures us that he will go on while strength (would we could add health) remains. The vast amount of such work he has already accomplished might overtax the powers of the strongest. That it could have been done at all under constant infirm health is most wonderful.

X

INSECTIVOROUS PLANTS

(The Nation, April 2 and 9, 1874)

That animals should feed upon plants is natural and normal, and the reverse seems impossible. But the adage, "Natura non agit saltatim," has its application even here. It is the naturalist, rather than Nature, that draws hard and fast lines everywhere, and marks out abrupt boundaries where she shades off with gradations. However opposite the parts which animals and vegetables play in the economy of the world as the two opposed kingdoms of organic Nature, it is becoming more and more obvious that they are not only two contiguous kingdoms, but are parts of one whole--ant.i.thetical and complementary to each other, indeed; but such "thin part.i.tions do the bounds divide" that no definitions yet framed hold good without exception.

This is a world of transition in more senses than is commonly thought; and one of the lessons which the philosophical naturalist learns, or has to learn, is, that differences the most wide and real in the main, and the most essential, may nevertheless be here and there connected or bridged over by gradations. There is a limbo filled with organisms which never rise high enough in the scale to be manifestly either animal or plant, unless it may be said of some of them that they are each in turn and neither long. There are undoubted animals which produce the essential material of vegetable fabric, or build up a part of their structure of it, or elaborate the characteristic leaf-green which, under solar light, a.s.similates inorganic into organic matter, the most distinguishing function of vegetation. On the other hand, there are plants--microscopic, indeed, but unquestionable--which move spontaneously and freely around and among animals that are fixed and rooted. And, to come without further parley to the matter in hand, while the majority of animals feed directly upon plants, "for 'tis their nature to," there are plants which turn the tables and feed upon them. Some, being parasitic upon living animals, feed insidiously and furtively; these, although really cases in point, are not so extraordinary, and, as they belong to the lower orders, they are not much regarded, except for the harm they do. There are others, and those of the highest orders, which lure or entrap animals in ways which may well excite our special wonder--all the more so since we are now led to conclude that they not only capture but consume their prey.

As respects the two or three most notable instances, the conclusions which have been reached are among the very recent acquisitions of physiological science. Curiously enough, however, now that they are made out, it appears that they were in good part long ago attained, recorded, and mainly forgotten. The earlier observations and surmises shared the common fate of discoveries made before the time, or by those who were not sagacious enough to bring out their full meaning or importance. Vegetable morphology, dimly apprehended by Linnaeus, initiated by Casper Frederick Wolff, and again, independently in successive generations, by Goethe and by De Candolle, offers a parallel instance. The botanists of Goethe's day could not see any sense, advantage, or practical application, to be made of the proposition that the parts of a blossom answer to leaves; and so the study of h.o.m.ologies had long to wait. Until lately it appeared to be of no consequence whatever (except, perhaps, to the insects) whether Drosera and Sarracenia caught flies or not; and even Dionaea excited only unreflecting wonder as a vegetable anomaly. As if there were real anomalies in Nature, and some one plant possessed extraordinary powers denied to all others, and (as was supposed) of no importance to itself!

That most expert of fly-catchers, Dionaea, of which so much has been written and so little known until lately, came very near revealing its secret to Solander and Ellis a hundred years ago, and doubtless to John Bartram, our botanical pioneer, its C probable discoverer, who sent it to Europe. Ellis, in his published letter to Linnaeus, with which the history begins, described the structure and action of the living trap correctly; noticed that the irritability which called forth the quick movement closing the trap, entirely resided in the few small bristles of its upper face; that this whole surface was studded C with glands, which probably secreted a liquid; and that the trap did not open again when an insect was captured, even upon the death of the captive, although it opened very soon when nothing was caught, or when the irritation was caused by a bit of straw, or any such substance. It was Linnaeus who originated the contrary and erroneous statement, which has long prevailed in the books, that the trap reopened when the fatigued captive became quiet, and let it go; as if the plant caught flies in mere play and pastime! Linnaeus also omitted all allusion to a secreted liquid--which was justifiable, as. Ellis does not state that he had actually seen any; and, if he did see it, quite mistook its use, supposing it to be, like the nectar of flowers, a lure for insects, a bait for the trap. Whereas, in fact, the lure, if there be any, must be an odor (although nothing is perceptible to the human olfactories); for the liquid secreted by the glands never appears until the trap has closed upon some insect, and held it at least for some hours a prisoner.

Within twenty-four or forty-eight hours this glairy liquid is abundant, bathing and macerating the body of the perished insect. Its a.n.a.logue is not the nectar of flowers, but the saliva or the gastric juice!

The observations which compel such an inference are re-cent, and the substance of them may be briefly stated. The late Rev. Dr. M. A. Curtis (by whose death, two years ago, we lost one of our best botanists, and the master in his especial line, mycology), forty years and more ago resided at Wilmington, North Carolina, in the midst of the only district to which the Dionaea is native; and he published, in 1834, in the first volume of the "Journal of the Boston Society of Natural History," by far the best account of this singular plant which had then appeared. He remarks that "the little prisoner is not crushed and suddenly destroyed, as is sometimes supposed,"

for he had often liberated "captive flies and spiders, which sped away as fast as fear or joy could hasten them." But he neglected to state, although he must have noticed the fact, that the two sides of the trap, at first concave to the contained insect, at length flatten and close down firmly upon the prey, exerting no inconsiderable pressure, and insuring the death of any soft-bodied insect, if it had not already succ.u.mbed to the confinement and salivation. This last Dr. Curtis noticed, and first discerned its import, although he hesitated to p.r.o.nounce upon its universality. That the captured insects were in some way "made subservient to the nourishment of the plant" had been conjectured from the first. Dr.

Curtis "at times (and he might have always at the proper time) found them enveloped in a fluid of mucilaginous consistence, which seems to act as a solvent, the insects being more or less consumed in it." This was verified and the digestive character of the liquid well-nigh demonstrated six or seven years ago by Mr. Canby, of Wilmington, Delaware, who, upon a visit to the sister-town of North Carolina, and afterward at his home, followed up Dr. Curtis's suggestions with some capital observations and experiments.

These were published at Philadelphia in the tenth volume of Meehan's Gardeners' Monthly, August, i868; but they do not appear to have attracted the attention which they merited.

The points which Mr. Canby made out are, that this fluid is always poured out around the captured insect in due time, "if the leaf is in good condition and the prey suitable;" that it comes from the leaf itself, and not from the decomposing insect (for, when the trap caught a plum-curculio, the fluid was poured out while he was still alive, though very weak, and endeavoring, ineffectively, to eat his way out); that bits of raw beef, although sometimes rejected after a while, were generally acted upon in the same manner--i.e., closed down upon tightly, salvered with the liquid, dissolved mainly, and absorbed; so that, in fine, the fluid may well be said to be a.n.a.logous to the gastric juice of animals, dissolving the prey and rendering it fit for absorption by the leaf. Many leaves remain inactive or slowly die away after one meal; others reopen for a second and perhaps even a third capture, and are at least capable of digesting a second meal.

Before Mr. Canby's experiments had been made, we were aware that a similar series had been made in England by Mr. Darwin, with the same results, and with a small but highly-curious additional one--namely, that the fluid secreted in the trap of Dionaea, like the gastric juice, has an acid reaction. Having begun to mention unpublished results (too long allowed to remain so), it may be well, under the circ.u.mstances, to refer to a still more remarkable experiment by the same most sagacious investigator. By a p.r.i.c.k with a sharp lancet at a certain point, he has been able to paralyze one-half of the leaf-trap, so that it remained motionless under the stimulus to which the other half responded. Such high and sensitive organization entails corresponding ailments. Mr. Canby tells us that he gave to one of his Dionaea-subjects a fatal dyspepsia by feeding it with cheese; and under Mr. Darwin's hands another suffers from paraplegia.

Finally, Dr. Burdon-Sanderson's experiments, detailed at the last meeting of the British a.s.sociation for the Advancement of Science, show that the same electrical currents are developed upon the closing of the Dionaea-trap as in the contraction of a muscle.

If the Venus's Fly-trap stood alone, it would be doubly marvelous--first, on account of its carnivorous propensities, and then as const.i.tuting a real anomaly in organic Nature, to which nothing leads up. Before acquiescing in such a conclusion, the modern naturalist would scrutinize its relatives.

Now, the nearest relatives of our vegetable wonder are the sundews.

While Dionaea is as local in habitation as it is singular in structure and habits, the Droseras or sundews are widely diffused over the world and numerous in species. The two whose captivating habits have attracted attention abound in bogs all around the northern hemisphere. That flies are caught by them is a matter of common observation; but this was thought to be purely accidental. They spread out from the root a circle of small leaves, the upper face of which especially is beset and the margin fringed with stout bristles (or what seem to be such, although the structure is more complex), tipped by a secreting gland, which produces, while in vigorous state, a globule of clear liquid like a drop of dew-- whence the name, both Greek and English. One expects these seeming dew-drops to be dissipated by the morning sun; but they remain unaffected. A touch shows that the glistening drops are glutinous and extremely tenacious, as flies learn to their cost on alighting, perhaps to sip the tempting liquid, which acts first as a decoy and then like birdlime. A small fly is held so fast, and in its struggles comes in contact with so many of these glutinous globules, that it seldom escapes.

The result is much the same to the insect, whether captured in the trap of Dionaea or stuck fast to the limed bristles of Drosera. As there are various plants upon whose glandular hairs or glutinous surfaces small insects are habitually caught and perish, it might be pure coincidence that the most effectual arrangement of the kind happens to occur in the nearest relatives of Dionaea. Roth, a keen German botanist of the eighteenth century, was the first to detect, or at least to record, some evidence of intention in Drosera, and to compare its action with that of Dionaea, which, through Ellis's account, had shortly before been made known in Europe. He noticed the telling fact that not only the bristles which the unfortunate insect had come in contact with, but also the surrounding rows, before widely spreading, curved inward one by one, although they had not been touched, so as within a few hours to press their glutinous tips likewise against the body of the captive insect--thus doubling or quadrupling the bonds of the victim and (as we may now suspect) the surfaces through which some part of the animal substance may be imbibed. For Roth surmised that both these plants were, in their way, predaceous. He even observed that the disk of the Drosera-leaf itself often became concave and enveloped the prey. These facts, although mentioned now and then in some succeeding works, were generally forgotten, except that of the adhesion of small insects to the leaves of sundews, which must have been observed in every generation. Up to and even within a few years past, if any reference was made to these a.s.serted movements (as by such eminent physiologists as Meyen and Trevira.n.u.s) it was to discredit them. Not because they are difficult to verify, but because, being naturally thought improbable, it was easier to deny or ignore them. So completely had the knowledge of almost a century ago died out in later years that, when the subject was taken up anew in our days by Mr. Darwin, he had, as we remember, to advertise for it, by sending a "note and query" to the magazines, asking where any account of the fly-catching of the leaves of sundew was recorded.

When Mr. Darwin takes a matter of this sort in hand, he is not likely to leave it where he found it. He not only confirmed all Roth's observations as to the incurving of the bristles toward and upon an insect entangled on any part of the disk of the leaf, but also found that they responded similarly to a bit of muscle or other animal substance, while to any particles of inorganic matter they were nearly indifferent. To minute fragments of carbonate of ammonia, however, they were more responsive. As these remarkable results, attained (as we are able to attest) half a dozen years ago, remained unpublished (being portions of an investigation not yet completed), it would have been hardly proper to mention them, were it not that independent observers were beginning to bring out the same or similar facts. Mrs. Treat, of New Jersey, noticed the habitual infolding of the leaf in the longer-leaved species of sundew (American Journal of Science for November, 1871), as was then thought for the first time--Roth's and Withering's observations not having been looked up. In recording this, the next year, in a very little book, ent.i.tled "How Plants Behave," the opportunity was taken to mention, in the briefest way, the capital discovery of Mr. Darwin that the leaves of Drosera act differently when different objects are placed upon them, the bristles closing upon a particle of raw meat as upon a living insect, while to a particle of chalk or wood they are nearly inactive. The same facts were independently brought out by Mr. A. W. Bennett at the last year's meeting of the British a.s.sociation for the Advancement of Science, and have been mentioned in the journals.

If to these statements, which we may certify, were added some far more extraordinary ones, communicated to the French Academy of Science in May last by M. Zeigler, a stranger story of discrimination on the part of sundew-bristles would be told. But it is safer to wait for the report of the committee to which these marvels were referred, and conclude this sufficiently "strange eventful history" with some details of experiments made last summer by Mrs. Treat, of New Jersey, and published in the December number of the American Naturalist. It is well to note that Mrs. Treat selects for publication the observations of one particular day in July, when the sundew-leaves were unusually active; for their moods vary with the weather, and also in other unaccountable ways, although in general the sultrier days are the most appetizing:

"At fifteen minutes past ten of the same day I placed bits of raw beef on some of the most vigorous leaves of Drosera longifolia. Ten minutes past twelve, two of the leaves had folded around the beef, hiding it from sight.

Half-past eleven of the same day, I placed living flies on the leaves of D.

longifolia. At 12 and 48 minutes one of the leaves had folded entirely around its victim, the other leaves had partially folded, and the flies had ceased to struggle. By 2 and 30 minutes four leaves had each folded around a fly. . . . I tried mineral substances--bits of dry chalk, magnesia, and pebbles. In twenty-four hours, neither the leaves nor their bristles had made any move like clasping these articles. I wet a piece of chalk in water, and in less than an hour the bristles were curving about it, but soon unfolded again, leaving the chalk free on the blade of the leaf.

Parallel experiments made on D. rotundifolia, with bits of beef and of chalk, gave the same results as to the action of the bristles; while with a piece of raw apple, after eleven hours, "part of the bristles were clasping it, but not so closely as the beef," and in twenty-four hours "nearly all the bristles were curved toward it, but not many of the glands were touching it."