108 



HUTCHINSON'S POPULAR BOTANY 



absorption. This takes place in the stomach. It also is a fermentation 

 that is, a chemical change effected by the agency of a leaven or ferment 

 which is contained in the stomach juice, and can be, like the ferment of 

 saliva, easily separated and prepared. As so separated, it is called pepsin. 



" Between this process and the digestion of the Dioncea leaf the resem- 

 blance is complete. It digests exactly the same substances in exactly the 

 same way i.e. it digests the albuminous constituents of the bodies of 

 animals just as we digest them. In both instances it is essential that the 

 body to be digested should be steeped in a liquid, which in Dioncea is 

 secreted by the red glands on the upper surface of the leaf ; in the other 

 case by the glands of the mucous membrane. In both, the act of secretion 

 is excited by the presence of the substance to be digested. In the leaf, just 

 as in the stomach, the secretion is not poured out unless there is something 

 nutritious in it for it to act upon ; and, finally, in both cases the secretion is 

 acid. As regards the stomach, we know what the acid is it is hydrochloric 

 acid. As regards the leaf, we do not know precisely as yet, but Mr. Darwin 

 has been able to arrive at very probable conclusions." 



These ferments are now known as " enzymes," and those that digest 



proteids are distinguished as 

 " proteases." Of the proteases 

 three kinds are known, under 

 the names of pepsin, trypsin, and 

 erepsin. Pepsin, as Sanderson 

 points out, acts only in an acid 

 solution, but trypsin and erepsin 

 are most active in alkaline 

 liquids. Professor Vines and 

 others have shown the presence 

 of one or other of these en- 

 zymes in the germinating seeds 

 of a variety of plants, and de- 

 monstrated the probability of a 

 protease of some kind being pre- 

 sent in all plants at one stage or 

 another of their development. 

 It appears that the digestive pro- 

 cesses are essentially the same 

 in both animals and plants. 



The Butterworts (Pingui- 

 cudci) constitute another genus 

 of insectivorous plants. One 



FIG. 142,-CoMMON BLADDEBWOBT species, Pinguicula vulgaris, 



( Utricularia vulgaris). better known as the Bog-violet 



Above, one of the bladders is shown greatly magnified. Or Large ButterWOrt, is Common 



