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Show 378 PINGUICULA VULGARIS. CHAP. XVI. complete re-expansion in 16 hrs. 30m. Nitrogenous fluids act for a shorter time than nitrogenous substances · thus when drops of an infusion of raw meat were pl' aced 'o n the midrib of a leaf, the incurved 1narcrins began to unfold in only 10 hrs. 37 1n., and this b was the quickest act of re-expans1. on ob served by me; but it may have been partly due to the distance of the margins from the midrib where the drops lay. \V e are naturally led to inquire what is the use of this movement which lasts for so short a time? If very small objects, such as fibres of 1neat, or moderately small objects, such as little flies or cabbage-seeds, are placed close to the margin, they are either completely or partially ·embraced by it. The glands of the overlapping margin 'are thus brought into contact with such objects and pour forth their secretion, afterwards absorbing the digested matter. But as the incurvation lasts for so short a ti1ne, any such benefit can be of only slight importance, yet perhaps greater than at first appears. The plant lives in humid districts, and the insects which adhere to all parts of the leaf are wa~hed by every heavy shower of rain into the narrow channel formed by the naturally incurved edges. For instance, my friend in North Wales placed several insects on so1ne leaves, and two days afterwards (there having been heavy rain in the interval) found some of them quite washed away, and many others safely tucked under the now closely infloctQd margins, the glands of which all round the insects were no doubt secreting. We can thus, also, understand how it is that so many insects, and fragm{3nts of insects, are generally found 1 ying within the incurved margins of the leaves. The incurvation of the n1argin, due to the presence of an exciting object, must be serviceable in another CHAP. XVI. MOVEMENTS OF THE LEAVES. 379 and probably more important way. We have seen that when large bits of meat, or of sponge soaked in the juice of meat, were placed on a loaf, tho margin was not able to embrace them, but, as it became incurved, pushed them very slowly towards the middle of the leaf, to a distance from the outside of fully ·I of an inch (2·54 mm.), that is, across betw en one-third and one-fourth of the space between the edge and mi lrib. Any object, such as a moderately sized insect, would thus be brought slowly into contact with a far larger number of glands, inducing much more secretion and absorption, than would otherwise have been the case. That this would be highly serviceable to the plant, we may infer from the fact that Drosera has acquired highly developed powers of movement, merely for the sake of bringing all its glands i<hto contact with captured insects. So again, after a leaf of Dionooa has caught an insect, the slow pressing together of the two lobes serves 1nerel y to bring the glands on both sides into contact with it, causing also the secretion charged with animal matter to spread by capillary attraction over the whole surface. In the case of Pinguicula, as soon as an insect has been pushed for some little distance towards the midrib, immediate re-expansion would be beneficial, as the margins could not capture fresh prey until they were unfolded. The service rendered by this pushing action, as well as that from the marginal glands being brought into contact for a short time with the upper surfaces of minute captured insects, may perhaps account for the peculiar movements of the leaves; otherwise, we must look at these movements as a remnant of a more highly developed power formerly possessed by the progenitors of the genus. · In the four British species, and, as I hear from |