Page:Insectivorous Plants, Darwin, 1899.djvu/35

 limited, or quite deficient, unless the plant had the power of obtaining this important element from captured insects. We can thus understand how it is that the roots are so poorly developed. These usually consist of only two or three slightly divided branches from half to one inch in length, furnished with absorbent hairs. It appears, therefore, that the roots serve only to imbibe water; though, no doubt, they would absorb nutritious matter if present in the soil ; for as we shall hereafter see, they absorb a weak solution of carbonate of ammonia. A plant of Drosera, with the edges of its leaves curled inwards, so as to form a temporary stomach, with the glands of the closely inflected tentacles pouring forth their acid secretion, which dissolves animal matter, afterwards to be absorbed, may be said to feed like an animal. But, differently from an animal, it drinks by means of its roots ; and it must drink largely, so as to retain many drops of viscid fluid round the glands, sometimes as many as 260, exposed during the whole day to a glaring sun.

[Since the publication of the first edition, several experiments have been made to determine whether insectivorous plants are able to profit by an animal diet.

My experiments were published in 'Linnean Society's Journal,' and almost simultaneously the results of Kellermann and Von Raumer were given in the 'Botanische Zeitung.' My experiments were begun in June 1877, when the plants were collected and planted in six ordinary soup-plates. Each plaie was divided by a low partition into two sets, and the least flourishing half of each culture was selected to be " fed," while the rest of the plants were destined to be " starved." The plants were prevented from catching insects for themselves by means of a covering of fine gauze, so that the only animal food which they obtained was supplied in very minute pieces of roast meat given to the "fed" plants but withheld from the "starved" ones. After only ten days the difference between the fed and starved plants was clearly visible: the fed plants were of brighter green and the tentacles of a more lively red. At the end of August the plants