156 CARNIVOROUS PLANTS WITH ADHESIVE Al'1'ARATUS. 



plants and species of the caper order (c.c/. tiaponaria viscosa, Silene viscosa, Oleome 

 ornithopodioides, Bonchea cohiteoides), and lastly, a series of plants which fltnirish 

 in peat-bogs and upon deep beds of humus, such as Sedo/m villosiim,, Roridula 

 dentata, Byhlis gitjantea, and many others besides. 



It would, however, be erroneous to suppose that in all cases where a sticky 

 coating occurs on leaves and stem a solution and digestion of the insects adhering 

 to the viscid jjarts is necessarily denoted. In many instances structures of this 

 kind, which are analogous to lime-twigs, are a means of protecting honey-bearing 

 flowers against unwelcome guests belonging to the world of insects, as will be 

 explained in greater detail later on. Glands secreting a viscid substance may, no 

 doubt, often possess two kinds of function — they may, on the one hand, prevent 

 unbidden animals from appi-oaching the honey, and, on the other, turn to advantage 

 such insects as are tempted by immoderate craving to step upon the perilous path 

 leading to the honey-receptacles and so adhere to it and die, by dissolving their 

 flesh and blood with the aid of the secretion and then absorbing them. 



Many plants have, on the epidermis of their leaves, structures corresponding in 

 form to the glands of insectivorous plants, but which do not discharge secretions 

 either spontaneously or when irritated. On the other hand, these structures have 

 the power of imbibing water, and are, in this relation, of the gi-eatest importance 

 to the plants in question. Although the more detailed treatment of them is post- 

 poned until we have occasion to deal with the absorption of water by aerial organs, 

 it is advisable to refer now to the fact that chemically pure water only very rarely 

 reaches the interior of a plant by means of the absorptive organs mentioned. 

 Sulphuric acid is almost always introduced with atmospheric w^ater, and in some 

 circumstances annnonia also. However trivial the amount of the nitrogen con- 

 veyed to plants in this way, it must not be undervalued, at all events in the case 

 of those which are only able to acquire small quantities of nitrogenous compounds 

 from the ground by means of their roots. Now, it is very probable that plants of 

 this kind do not reject even other nitrogenous compounds which are brought 

 with the water from the atmosphere to their aerial lea\-e8. The foliage-leaves of 

 many plants display contrivances whereby rain-water is often retained for a 

 considerable time in special hollows. In these depressions thei'e is invariably a 

 collection of dust-particles, small dead animals, pollen-grains, &c., which have been 

 blown in by the wind, whilst rain trickling down the stem brings very various 

 objects with it from higher up and w-ashes them into these reservoirs in the leaves. 

 Sometimes too a few animals are drowned in the water-receptacles. As a matter 

 of fact, the water in the hollows of the leaves of the Peltate Saxifrage and of 

 Bromeliacese, in tlie inflated vaginae of many umbelliferous plants, and in the 

 cups formed by the coalescence of opposite leaves in many Gentianeaj, Compo.sitae, 

 and Dipsacese, is always brown-coloured, and contains nitrogenous compounds in 

 solution, derived from the decaying bodies of dead animals which have fallen into 

 these receptacles. 



If absorbent organs are present in the reservoirs in question, the w-ater, together 



