Concluding Remarks.—The leaves of the three foregoing closely allied species or varieties are manifestly adapted for catching living creatures. With respect to the functions of the several parts, there can be little doubt that the long jointed hairs are sensitive, like those of Dionaea, and that, when touched, they cause the lobes to close. That the glands secrete a true digestive fluid and afterwards absorb the digested matter, is highly probable from the analogy of Dionaea,—from the limpid fluid within their cells being aggregated into spherical masses, after they had absorbed an infusion of raw meat,—from their opaque and granular condition in the leaf, which had enclosed a beetle for a long time,—and from the clean condition of the integuments of this insect, as well as of crustaceans (as described by Cohn), which have been long captured. Again, from the effect produced on the quadrifid processes by an immersion for 24 hrs. in a solution of urea,—from the presence of brown granular matter within the quadrifids of the leaf in which the beetle had been caught,—and from the analogy of Utricularia,—it is probable that these processes absorb excrementitious and decaying animal matter. It is a more curious fact that the points on [page 331] the infolded margins apparently serve to absorb decayed animal matter in the same manner as the quadrifids. We can thus understand the meaning of the infolded margins of the lobes furnished with delicate points directed inwards, and of the broad, flat, outer portions, bearing quadrifid processes; for these surfaces must be liable to be irrigated by foul water flowing from the concavity of the leaf when it contains dead animals. This would follow from various causes,—from the gradual contraction of the concavity,—from fluid in excess being secreted,—and from the generation of bubbles of air. More observations are requisite on this head; but if this view is correct, we have the remarkable case of different parts of the same leaf serving for very different purposes—one part for true digestion, and another for the absorption of decayed animal matter. We can thus also understand how, by the gradual loss of either power, a plant might be gradually adapted for the one function to the exclusion of the other; and it will hereafter be shown that two genera, namely Pinguicula and Utricularia, belonging to the same family, have been adapted for these two different functions. [page 332] CHAPTER XV. DROSOPHYLLUM—RORIDULA—BYBLIS—GLANDULAR HAIRS OF OTHER PLANTS—CONCLUDING REMARKS ON THE DROSERACEÆ. Drosophyllum—Structure of leaves—Nature of the secretion—Manner of catching insects— Power of absorption—Digestion of animal substances—Summary on Drosophyllum—Roridula—Byblis—Glandular hairs of other plants, their power of absorption—Saxifraga—Primula— Pelargonium—Erica—Mirabilis—Nicotiana—Summary on glandular hairs—Concluding remarks on the Droseraceae.