456 MANUAL OF BOTANY 



and trypsin convert albumins and globulins into peptones, the 

 latter decomposing peptone into amide bodies. Rennet is pro- 

 bably a member of this group, but its function in vegetable 

 metabolism is unknown. It possesses the power of clotting 

 milk. The enzymes acting upon glucosides are many ; the best 

 known are emulsin, myrosin, erythrozyni, and rhdvinase. The 

 fourth class has only one member which has been investigated at 

 present, the glyceride enzyn:ie that decomposes castor oil. 



Diastase appears to exist in two varieties, distinguished from 

 each other by their mode of action on the starch grain. One, 

 called diastase of translocation, dissolves the grain slowly from 

 w^ithout inwards ; the other, diastase of sfrrefioT?, disintegrates 

 it by a process of corrosion before dissolving it. The first of 

 these varieties has a very wide distribution in plants, being 

 present almost everywhere. The second is the body formed by 

 the glandular epithelium of the scutellum of the grasses. 



The great function of diastase in the plant is to transform 

 starch (and probably glycogen where it occurs) into maltose, or 

 malt sugar. Wherever starch is formed, whether in the living 

 leaf or in the reservoir set apart for storage, it must be regarded 

 as a reserve material. It has a rather large molecule, but 

 its exact formula is not thoroughly known. The formula 

 n (0,;H.,,0-,) is taken to represent it, and the value of n is 

 probably 5. The starch molecule is possiblj^ composed of four 

 amylin or dextrin-like groups, arranged about a fifth. It has 

 been suggested that the first action of ihe diastase is the libera- 

 tion of them from each other; and that four of them, by succes- 

 sive incorporation of water, are converted through a series of 

 malto-dextrins into maltose, while the fifth withstands the action 

 of the enzyme for a considerable time. After the enzyme has 

 been acting for a short time the resulting product is found to be 

 four parts maltose and one part dextrin. How far this series of 

 decompositions represents w^iat takes place in the plant is un- 

 certain, but it is clear that the starch, which is insoluble, is 

 converted into sugar, which can be removed to the part of the 

 plant where it is required for building up the protoplasm. 



Inulase occurs only in the tubers and roots of some of the 

 Compositae, where inulin is abundant. It appears to convert 

 inulin into levulose, an intermediate body being formed in the 

 process. Invertase is easily extracted from the Yeast plant; in 

 which it is abundant. In flowering plants it has been found 

 in the seeds, buds and leaves, and pollen grains. In other fungi 

 than Saccharomyces it occurs in Fusarum and Asj^ergillus, 



