THE METABOLISM OF PLANTS. 19 1 



formed by means of a proteolytic ferment. There is, however, 

 no positive evidence forthcoming in support of this view. 

 Finally there is probably, in certain plants at least, a ferment 

 which acts upon cellulose, converting it into sugar. For 

 instance, we have seen that carbohydrate is stored up in the 

 Date-seed in the form of cellulose, and that this cellulose is 

 used up during germination in supplying the embryo with 

 plastic material; it is difficult to imagine that the solution 

 of the cellulose is brought about otherwise than by ferment- 

 action. The penetration of the absorbent organs of parasites 

 into the tissues of their hosts is probably effected by the 

 same means. 



We have now to enquire into the nature of the chemical 

 processes of which the decompositions enumerated above are 

 the result. The mode of action of unorganised ferments is 

 that they induce chemical change in the substance upon 

 which they act without themselves entering into or being 

 affected by the process. The change which they effect is 

 probably, in the first instance, one of hydration, that is, the 

 addition of one or more molecules of water to the molecule 

 of the substance acted upon ; this appears to diminish the 

 stability of the substance so that its molecules readily disso- 

 ciate to form two or more other substances. 



The following examples will serve to illustrate ferment-action : 

 i, the conversion of starch into sugar by diastase ; 



the relation of the quantity of the products to each other and to the 

 starch has been found to vary with the temperature ; the equations here 

 given represent what takes place at ordinary temperatures (below 6oC). 

 The conversion takes place in two stages ; 



Maltose. Dextrin. 



a, 3 (C 6 H 10 6 ) + H 2 = C 12 H 22 O U + C 6 H 10 O 6 ; 



Dextrin. Maltose. 



, 2 (C 6 H 10 O 5 ) + H 2 O = CiaH^Ou (von Mering) ; 



if the action be long continued the maltose is converted into dextrose 

 according to O'Sullivan, 



CuHaOu + H 2 - 2 (C 6 H 12 6 ), 

 but Brown and Heron have failed to confirm this statement. 



