Popular Science Monthly/Volume 23/July 1883/Insectivorous Plants
IT was, I think, during the summer of 1876 that Mr. Darwin's most interesting work on "Insectivorous Plants" fell into my hands, and was read with the delight which the "fairy-tales of science" that came from his hand must ever inspire. As a matter of course, I procured, at once, some plants of the Drosera rotundifolia, and began a series of amateur experiments, which were to me so interesting that I began to wish all plants might have been created with the same marvelous properties.
While my mind was thus employed, I began to notice that the plants of the common garden Petunia (P. grandiflora) were almost always quite freely powdered with the dead or apparently dying bodies of small insects, which seemed to be held fast, either by the hairs with which every part of this plant is covered, or by the gummy, sweetish exudations therefrom. I made pilgrimages to other gardens than our own, invariably finding the petunia-plants covered with the small captives. It was not until the summer of 1881 that I had access to a good microscope, since which time I have spent many hours in trying to penetrate this mystery. In this I have been greatly assisted by ray friend Dr. J. H. W. Meyer, who was at first very skeptical in regard to my confident assertions that here was a new insectivorous plant, but who grew more and more interested, and finally became an enthusiastic convert.
Upon our first examination, we found that the hairs—tentacles we have learned to call them—varied in length, were somewhat thickened at the base, usually three-celled, the last cell being expanded into a spherical shape. Small protuberances were often found upon the sides of the hairs (Fig. 1), but more commonly upon the bulbous tip. Sometimes these cells seemed to me to have a decidedly spiral form, but of this I could never be quite sure. The tentacles were extremely flexible, sometimes turning sharply backward, as in Fig. 2.
I have made many observations, with a hand-magnifier, upon the plants in the garden. I found the freshly captured insects most plentiful
about nightfall, at which time the petunia-blossoms emit a powerful odor, and the clamminess of the leaves and stems is most noticeable. I have seen insects as large as the common red ant struggle and die, and have found the horny wings of small Coleoptera, but most frequently I have found small spiders, gnats, etc.
When an insect alights upon a leaf (I say leaf, although the hairs upon the stems, calyxes, and even the outer and lower portions of the flower-tubes are quite as vigorous, and as often successful), it at first manifests much alarm, runs with as much strength as possible up and down and under the leaf, lifting its feet with more and more of an effort, until at last, either benumbed or exhausted, its motions are almost imperceptible, and sometimes for an hour will occur at such long intervals that one decides half a dozen times that death must already have taken place. On one occasion, a branch bearing a lively little insect was cut from the plant, put into water, and the leaf on which the insect was struggling placed under the microscope about six o'clock in the evening, and watched until eleven, by which time life was undoubtedly extinct. During these hours the fight for existence was most interesting, the tentacles one by one discharging their fluid, first by casting drops between the wings—an almost invariable proceeding—thus destroying their usefulness by gumming them firmly together (as in Figs. 3, 4). Then the tips of the tentacles, by this
|Fig. 6.||Fig. 7.||Fig. 8.|
time so much excited as to have quite lost their spherical form, are inserted between the joints about the head, and among the hairs of the feet and legs (as in Figs. 5, 6, 7), the stronger members being firmly pinioned by the stronger tentacles (as Fig. 8), while the small hairs are discharging their fluid. This fluid seems to be somewhat tenacious.
Small seeds and bits of sand are sometimes caught in the same manner, but rather daintily, as if the plant merely wished to see if it were worth while or not (as in Fig. 9). I have never seen them inclosed by the hairs, as are the animal substances.
These are some of the things that I have seen. I do not know what may be the motive of the plant; what it does with the insect, the last stage of whose strange eventful history I have so often seen in a dry, withered carcass, or a few detached and macerated limbs (Fig. 10). I do know, however, that the plant begins its depredatory career as early as the unfolding of the second pair of leaves from the cotyledons, and continues it up to the time of the first frosts.
And so, having come to where, for me, the "thus far" ends and the "no farther" begins, I beg to call the attention of those interested in insectivorous plants to the Petunia, which fills every waste place in our gardens.