88 THE VEGETATIVE FUNCTIONS OF .PLANTS 



lium of the embryo. Often this glandular layer is in- 

 vaginated, so as to form a true gland (Fig. 62). 



A special case of plant nutrition is presented by the 

 insectivorous plants, of which there are many kinds. 

 They are all characterized by the possession of some de- 

 vice for capturing insects that visit them, and by the 

 ability to secrete a proteolytic enzyme capable of digest- 

 ing the protein tissues of their prey. These plants can 

 also digest any meat fed to them artificially. After 

 being digested the protein food is absorbed by osmosis. 

 The Venus's flytrap {Dionaa muscipula), numerous 

 species of bladderwort (Utricularia), and several species 

 of sundew (Drosera) serve to illustrate the insectivorous 

 plants (Figs. 63-65). Although these plants are able 

 to digest protein, experiments have shown that a pro- 

 tein diet is not necessary either for their life or healthy 

 growth. 



86. Assimilation. — After food has been elaborated and 

 digested it still is not a part of the living protoplasm, but 

 only lies within the vacuoles of the protoplast. It is no 

 more a part of the plant than is food in our hands or 

 stomachs a part of our bodies. One step more is nec- 

 essary; the digested food must be incorporated into, and 

 made part of, the living protoplasm itself. It must be 

 transformed from lifeless matter into living matter. As 

 in the case of enzyme action, the process by which this 

 remarkable change is brought about is not understood. 

 By multitudes of accurate, painstaking experiments, 

 however, one great fundamental truth has been estabHshed, 

 namely, that non-living matter can be converted into 

 living matter only by the action of other Kving matter 

 already existing. Proteins, sugars, and fats have all 



