Page:Insectivorous Plants, Darwin, 1899.djvu/91

 Chap. VI.] DIGESTION. 71

CHAPTER VI.

THE DIGESTIVE POWER OF THE SECRETION OF DROSERA.

The secretion rendered acid by the direct and indirect excitement of the glands - Nature of the acid - Digestible substances Albumen, its digestion arrested by alkalies, recommences by the addition of an acid - Meat - Fibrin Syntonin Areolar tissue Cartilage Fibro-cartilage - Bone - Enamel and dentine - Phosphate of lime - Fibrous basis of bone - Gelatine - Chondrin - Milk, casein and cheese - Gluten - Legumin - Pollen - Globulin - Haematin - Indigestible substances - Epidermic productions - Fibro-elastic tissue - Mucin - Pepsin - Urea - Chitine - Cellulose - Gun-cotton - Chlorophyll - Fat and oil - Starch - Action of the secretion on living seeds - Summary and concluding remarks.

As we have seen that nitrogenous fluids act very differently on the leaves of Drosera from non-nitrogenous fluids, and as the leaves remain clasped for a much longer time over various organic bodies than over inorganic bodies, such as bits of glass, cinder, wood, &c., it becomes an interesting inquiry, whether they can only absorb matters already in solution, or render it soluble, that is, have the power of digestion. We shall immediately see that they certainly have this power, and that they act on albuminous compounds in exactly the same manner as does the gastric juice of mammals; the digested matter being afterwards absorbed. This fact, which will be clearly proved, is a wonderful one in the physiology of plants. I must here state that I have been aided throughout all my later experiments by many valuable suggestions and assistance given me with the greatest kindness by Dr. Burdon Sanderson.

It may be well to premise for the sake of any reader who knows nothing about the digestion of albuminous compounds by animals that this is effected by means of a ferment, pep- sin, together with weak hydrochloric acid, though almost any acid will serve. Yet neither pepsin nor an acid by itself has any such power. We have seen that when the glands of