206 Elementary Biology. 



turned into soluble substances, before they can be circulated. 

 This alteration of substances so as to make them soluble is 

 known as metastasis, and is brought about by means of 

 compounds produced by the plant itself which are known 

 as ferments. There are four chief kinds of ferments 

 known : the first is termed the diastatic ferment, its func- 

 tion being to render starch soluble ; this it does by trans- 

 forming it into sugar. The second, the proteolytic ferment, 

 has for its function the transformation of proteids into 

 peptones (soluble proteids) in the presence of an acid. The 

 other two ferments are less important : one has for its func- 

 tion the decomposing of substances known as glucosides 

 (compounds of sugar with some aromatic principle), the 

 other the converting of cane into grape sugar. All four 

 perform their function in the same way, viz. by hydration 

 (p. 23), the ferment itself not being altered in the process. 



The paths by which these various products of fermenta- 

 tion move may be summarised thus : 



(a) By osmosis, from cell to cell in the parenchyma. 



(b) By intercellular communication of protoplasm in 



sieve tubes (and doubtless many other tissues). 



(<r) By laticiferous vessels. 



The object of this circulation is twofold, viz. to supply 

 plastic material wherewith t3 build up new protoplasm, 

 and to carry material to storehouses in the stem, or root, 

 or other parts of the plants. In these stores the food-stuffs 

 are modified again into insoluble forms, such as starch, oil, 

 aleurone and various amides. They are again transformed 

 into soluble carbohydrates and proteids as they are wanted, 

 and transferred up the stem to the seat of anabolic activity. 

 This storage of plastic material in an insoluble form is the 

 visible expression of the transformation of kinetic into 

 potential energy ; while the reconversion of the insoluble 

 store into soluble plastic material is the first step in the 

 transformation of the potential energy of the stored food 

 into kinetic energy. Both transformations are accom- 



