From the foregoing experiments and observations we [page 389] see that objects not containing soluble matter have little or no power of exciting the glands to secrete.  Non-nitrogenous fluids, if dense, cause the glands to pour forth a large supply of viscid fluid, but this is not in the least acid.  On the other hand, the secretion from glands excited by contact with nitrogenous solids or liquids is invariably acid, and is so copious that it often runs down the leaves and collects within the naturally incurved margins.  The secretion in this state has the power of quickly dissolving, that is of digesting, the muscles of insects, meat, cartilage, albumen, fibrin, gelatine, and casein as it exists in the curds of milk.  The glands are strongly excited by chemically prepared casein and gluten; but these substances (the latter not having been soaked in weak hydrochloric acid) are only partially dissolved, as was likewise the case with Drosera.  The secretion, when containing animal matter in solution, whether derived from solids or from liquids, such as an infusion of raw meat, milk, or a weak solution of carbonate of ammonia, is quickly absorbed; and the glands, which were before limpid and of a greenish colour, become brownish and contain masses of aggregated granular matter.  This matter, from its spontaneous movements, no doubt consists of protoplasm.  No such effect is produced by the action of non-nitrogenous fluids.  After the glands have been excited to secrete freely, they cease for a time to secrete, but begin again in the course of a few days.

Glands in contact with pollen, the leaves of other plants, and various kinds of seeds, pour forth much acid secretion, and afterwards absorb matter probably of an albuminous nature from them.  Nor can the benefit thus derived be insignificant, for a considerable [page 390] amount of pollen must be blown from the many wind-fertilised carices, grasses, &c., growing where Pinguicula lives, on to the leaves thickly covered with viscid glands and forming large rosettes.  Even a few grains of pollen on a single gland causes it to secrete copiously.  We have also seen how frequently the small leaves of Erica tetralix and of other plants, as well as various kinds of seeds and fruits, especially of Carex, adhere to the leaves.  One leaf of the Pinguicula had caught ten of the little leaves of the Erica; and three leaves on the same plant had each caught a seed.  Seeds subjected to the action of the secretion are sometimes killed, or the seedlings injured.  We may, therefore, conclude that Pinguicula vulgaris, with its small roots, is not only supported to a large extent by the extraordinary number of insects which it habitually captures, but likewise draws some nourishment from the pollen, leaves, and seeds of other plants which often adhere to its leaves.  It is therefore partly a vegetable as well as an animal feeder.

Pinguiculagrandiflora.