This section is from the book "The Gardener's Monthly And Horticulturist V21", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Mr. Henderson's statement of his experiment with the plants of Dionaea muscipula is not fully satisfactory. So far as the operation affected the growth and condition of the plants, the opinion of Mr. H. and his numerous friends is decisive, and there he makes a point; the "feeding" did not increase the size or the apparent vigor of the plants. This conclusion does not correspond to that of the Darwins, father and son, and which was one of the subjects of test by the experiment. According to the quotation of Mr. H., there were two positions of the Darwins which he proposed to test; first, "that the so-called carnivorous plants do make use as food of the insects they catch;" and, secondly, "that the difference in growth and final product were very much in favor of the meat-fed plants".
The second position, as we have seen, was not corroborated by the experiment; but how about the first one? Mr. H. narrates an incident in connection with his friend Mr. Smith, "a thorough believer in the carnivorous plant doctrine," who showed him " beyond question a minute species of shell-snails embedded in almost every one of the closed up leaf-traps of the Dionaeas. 'There,' says he, 'nature has placed the food-the animal food-directly into the mouths of these insect-eating plants. Can you longer doubt the correctness of Darwin's theory?'" Mr. H. says, "I was staggered but not yet convinced, and resolved to keep a close watch on the shell-snails ' that nature had placed in the mouths of these insect-eating plants.' Very soon they required no magnifying glass to see them; in three weeks they had increased wonderfully in breadth and stature; in three weeks more the biters were bitten, for the snails had eaten the fly-traps almost completely up. Mr. Smith has probably somewhat changed his base on the subject of 'carnivorous plants,' particularly as regards their use of shell-snails as an article of diet." Does Mr. H. intend to convey the idea that the Dionraea plants are not carnivorous, or only that shell-snails are not consumed by them? Evidently the impression conveyed is that they are not carnivorous, especially as he speaks of his ••prejudices against a theory that seems to reverse the whole order of nature." Why does not Mr. H. give all the facts? He had one hundred plants which were "' fed ' almost daily for three months with flies and other insects." "In this," he says, "I was assisted by one of my neighbors, a gentleman of leisure, and one who is well versed in many branches of natural science." The conditions for observation in this experiment were so favorable, it seems strange that Mr. H. should not make public more of the results.
All that we get is that, in the opinion of his friends and himself, the one hundred plants, to which the flies and other insects were given, were no larger or better looking, after three months of such treatment, than the one hundred plants which were screened so that no insects could visit them. From the remarks of Mr. H. we are in doubt whether the plants did in any sense assimilate or "feed" upon the insects. Now, the question is, did the plants "feed" on the insects? If they did Mr. H. must certainly know it; he can tell us how long it took a plant to consume a fly or other insect, and what was the appearance of the surface of the leaf while assimilation was progressing, if such was the case. If the plants did not "feed" on the insects, what became of the flies and other insects that were placed on the plants "almost daily for three months," by Mr. H. with the assistance of his neighbor? Three months is ninety-one days; each plant was fed "almost daily;" making a liberal allowance for days they were not fed, each plant must have received say from seventy-five to eighty "flies and other insects." Now, if these insects were not assimilated by the plants there must have been quite an accumulation of them upon the leaves at the end of the time.
If such were the case why should it have been expected that the plants might have received any benefit from such treatment, and why should Mr. H. be so careful as never to have omitted "an opportunity to ask professional horticulturalists their opinion" on this point? If the insects remained upon and about the plants, unappropriated by them, this ends the whole question-it could not have been supposed that they had received any benefit from the inseets. On the other hand, if the plants did "feed" upon the insects, the position of the Darwins on this point is confirmed, and the general drift of the conclusions of Mr. H. are incorrect; again, it would be a fair deduction, that the plants were nourished by the insects even if, as Mr. H. says, "the feeding did not certainly fatten." The fed plants and the non-fed plants did equally well, showing that they were able to procure their substance from the unorganized matter of the soil (sand and sphagnum), according to the usual "order of nature" or from the organized animal matter of "flies and other insects." The supply in either case was sufficient for the maximum demand of the plants; and when a supply was received from the insects a lessened demand was made upon the roots.
It is a subordinate question whether, under any circumstances, these plants will thrive better with animal food than without it. It is to be hoped, as "we are all after the truth in this matter," that Mr. H. will have the kindness to present all the facts in the case and then a proper conclusion may, perhaps, be reached.
Mr. Peter Henderson's account of his experiments in the December number of the Monthly in trying to demonstrate the truth or falsity of Mr. Francis Darwin's conclusions, are briefly as follows: Mr. Darwin cultivated a number of Sundews, one form of insect-eating plants, feeeding one-half with fibres of beef and not so feeding the rest, and when the plants were grown he counted and weighed the leaves and seeds, and also weighed the plants bodily, and in every case he found the advantage was on the side of the beef-fed plants. The leaves were more numerous, the flower stems taller and more vigorous, the flowers more numerous, the seeds more numerous-in every respect demonstrating that these plants did derive nourishment from this animal food. Now these are the facts as given on one side, which of course may be questioned by other careful investigators. Now let us examine closely the character of the plants experimented upon, and in them we may find more difference than in the character of the food or the care of the investigators, who are doubtless both correct in their facts.
It will be noticed Mr. Darwin experimented on Sundews, the common name of a species of Drosera, from droceros, dewy. These are an order of delicate herbaceous marsh plants of the south of Europe and ranging up to the tropics. There are about forty species of Drosera found in boggy places all over the world, except in the extremes of heat and cold. The Dionaea, or Fly-trap, is also placed in this order by many botanists. The Sundews, as commonly called, are remarkable for their singular red colored glandular hairs, which discharge a viscid acrid fluid in which insects are caught. The British species of the order with which Mr. Darwin doubtless experimented are all noted for this peculiarity, especially the variety often found near London and elsewhere, Drosera rotundifolia, or round-leaved Sundew; this has the leaves close to the ground, nearly circular and spreading, with a roundish limb tapering into a hairy petiole. Its secretions are very acrid and caustic, and in Italy the liquor called rossali is distilled from its juices. It curdles milk, and is said cures corns and warts.
Several of the foreign species have also the reputation of being poisonous, notably D. communis to sheep and cattle, while D. lunata has viscid leaves and glandular fringes which close upon insects happening to touch them, in this respect resembling Dionaea muscipula, but this is one of the exceptions in this class. While all are ornamented with red glandular hairs, discharging from their ends a drop of viscid acrid juice, the Drosera rotundifolia when seen luxuriating on living sphagnum moss in a cool house resembles an emerald set with a thousand little rubies, the beauty apparently enticing the insects which often become entangled on alighting and die.
Now I think the object of this is not difficult to understand. All decaying animal matter gives off ammonia, and a portion of this is no doubt decomposed by the plant to furnish the nitrogen which the plant requires. But as only a certain amount of this can be utilized by the plant, and if this amount can be obtained from the soil or surrounding air, any excess provided to the plant in the way of insects or flesh, could give no appreciable effects. So that the question of conditions of soil, may become an important factor as well as the difference in the nature of the plants. The power of catching insects is undisputed, but the object of this power and the utility of it, is the question which the consideration of the next plant Diona?a muscipula may assist us somewhat in reaching. This is the plant Mr. Henderson tried the effects of feeding with flies and other insects for several months, and as the feeding did not "fatten" it completely failed to sustain or corroborate Mr. Darwin's test. This plant is said to be originally from South America, although now found plentifully in North Carolina. There is but one species of this order, muscipula, a fly-trap. Its leaves which are spread out on the soil near the roots are composed of two parts, the one elongated and terminated by two rounded plates or leaves, furnished with hairs on their outer edge.
When touched these outer leaves close upon their victim and remain closed so long as the insect continues to struggle, but as soon as it is quiet the leaf opens and permits it to escape. These plates are also furnished with certain small glands in the upper surface whence exudes a viscuous liquid. But this does not appear to assist in retaining the animal. The retaining power in this instance being in the irritability of the plant acting on the nervure at the base, which is fashioned like a hinge, as when the efforts of the insect to escape ceases, irritability ends and the plant returns the two trap like nets to their former position. Should the fly or insect however continue its efforts to escape, the plant will remain shut until exhaustion or death prevents further movements against the sides of these singularly irritable leaves, which greatly resemble the sundews. The chief points of the differ-erence in the dionaea and the sundews are its in-dehiscent fruit, and erect aestivation and placenta placed at the base of a one-celled capsule, coupled with the extreme irritability of the glandular hairs which reaches its maximum in dionaea in this genera, and somewhat resembles the Mimosa sensitiva in the strange sensibility of its leaf which closes its folioles when the obscurity of night sets in, or when touched by a fly or other insect, the slightest touch sufficing to make its folioles close upon their supports.
In the Dionaea muscipula we have the phenomena of irritability under the influence of action only, displayed in a remarkable degree, and although it may properly be classed a carnivorous plant also, yet I do not think it a fair test to apply this variety standing alone as it were, either at the end, head, or on the dividing line of a group, to a large class of plants apparently differently constituted. The latter having beautiful leaves of spongy, cellular tissue, furnished with countless viscid glandular hairs, to attract, entangle and hold fast until death, the insect in the viscid fluid and retain the same until it has become decomposed and digested by the leaf in precisely the same way as digestion is carried on in the human frame; only as in case of necessity with us, another way of administering it as claimed by some of Mr. Darwin's followers. As already stated, no doubt both parties are correct and I only offer these remarks in the hope of harmonizing different effects from probably different causes, and trust that the best representatives of the European carnivora have not been put in competition or contrast with the poorest of the same class, but the only representative here.
I close with the suggestion to all investigators to make all conditions equal if possible, as it appears to me there is a reasonable doubt of this in the present case. Although I may be mistaken in my premises I submit matters as I view them.