458 MANUAL OF BOTANY 



These tryptic ferments, no doubt, bring about hydrolj'sis of the 

 proteid, though it is difficult to prove it by analysis. 



Whether rennet is proteolytic it is difficult to saj'. In the 

 animal body it effects a decomposition of one of the proteids of 

 milk, but the work it does in the plant has still to be ascertained. 

 It has a very wide distribution, existing in the fruits, flowers, 

 seeds, and shoots of various plants. 



The enzymes which decompose glucosides are numerous, and 

 are varied in their distribution. A typical one is the emulsin 

 of tlie bitter almond and cherry laurel, which splits up the 

 glucoside Amygdalin according to the equation 

 C,„H,,NO,, + 2H,0 = C,H,COH + HON + 2 (C,H,,0,) 



Amygilaliii. Water. Benzoic aldeliyile. Prussic acid. Sugar. 



This is, as in other cases, a process of hydrolysis. This enzyme 

 acts also on other glucosides. Myrosin, another of the group, 

 is peculiar in that it effects its decomposition without causing 

 the incorporation of water in the process ; thus : 



Cj„Hj,NKS,0,„ = CgH.CNS + C,Hj,0, + KHSO, 



Siuigrin. Sulpliocj'anate Sugar. Potassinm- 



of allyl. hydrogen 



sulpliate. 



Others, such as rhamnase, existing in the seeds of Bhammis 

 infectorius, erythrozym in the Madder, populin in the bark 

 of the Aspen, act similarly to emulsin on various glucosides. 



The digestion of the glucosides, we may notice, is always 

 accompanied by the formation of sugar, which is one of the 

 products of their decomposition. The fate of the other bodies 

 into which they split is not well ascertained, though there is 

 some evidence that cyanogen compounds, even such as hydro- 

 cyanic or prussic acid, are used for nutritive purposes by certain 

 plants. 



The digestion of fat or oil has not been very fully investi- 

 gated, though certain facts are known concerning its fate in 

 germinating seeds. The digestion is generally accompanied by 

 the production of starch grains in cells near the seat of diges- 

 tion, and it was formerly considered that the starch arose 

 directly from the oil. It appears now that the oil is split up 

 by an enzyme, with the formation of a free fatty acid and 

 glycerine. The fatty acid undergoes further decomposition, 

 being oxidised into simpler acid bodies which are crystalline 

 instead of being viscid like the fatty acid first liberated. These 

 pass into the general body of the seedling. The glycerine in its 

 turn is converted into some form of sugar, from which the 



