506 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



and old parts, and may be absent when young but appear later, or present when 

 young and subsequently disappear. An increase usually occurs during the mobiliza- 

 tion of reserve food-materials (Sect. 109), but for details concerning the occur- 

 rence, distribution, and translocation of ferments the reader is referred to the works 

 of Schleichert, A. Meyer, Fliigge, &C. 1 



Since diastatic ferments may also be concerned in the solution of cellulose 

 it is not surprising that they may occur in plants which do not produce starch, 

 as, for example, in most fungi, and it is probably owing to the adaption to special 

 nutritive conditions that no production of diastase can be detected in many 

 bacteria (Sect. 65). 



It does not necessarily follow that starch is only dissolved within the living 

 protoplast by the aid of diastase, simply because the process of solution follows 

 a similar course to that occurring externally 2 . No decisive evidence is afforded 

 either by the character of the products or by the possibility of regeneration. 



The different forms of diastase may be classified into a series of different 

 types, as, for example, into glucase, maltase, and granulase 3 , and of these only 

 glucase forms dextrose from starch. The other two produce maltose, with erythro- 

 dextrin as an intermediate product in the case of maltase, but isomaltose in that of 

 granulase. All three forms occasionally occur in the same plant, but even then the 

 embryo and the endosperm frequently contain different varieties of diastase. 

 Similarly, fungi probably produce more than one form of diastase, and bacteria 

 apparently also secrete those forms of diastase which act best in a weak alkaline 

 solution. Comparative researches into the action upon different starch-grains and 

 cell-walls will probably reveal further distinctions between the individual varieties 

 of diastase, and in the form of compounds the diosmotic and other properties may 

 be more or less markedly modified. 



Cytohydrolytic or cellulose-dissolving enzymes are probably frequently employed 

 to produce the dissolution or mucilaginous modification of cell-walls, as, for example, 

 during the penetration of fungi and other parasites which may bore through re- 

 sistant cellulose, or even through cuticularized or lignified walls. The fermentation 

 of cellulose may take place externally by the agency of bacteria, while within 

 the plant not only the hemi-celluloses deposited as reserve material, but also in 

 certain cases when copulation or cell-fusion occurs, typical cellulose walls may be 

 dissolved 4 . 



No detailed study has as yet been made of the different enzymes which decom- 

 pose cellulose, and it is uncertain whether all or only certain diastatic ferments 



1 See also Green, Annals of Botany, 1893, Vol. vn, p. 84; Griiss, Jahrb. f. wiss. Bot., 1894, 

 Bd. xxvi, p. 379, and Landw. Jahrb., 1896, Btl. xxv, p. 385; Beyerinck, Centralbl. f. Bact., 1893, 

 Abth. ii, Bd. I, pp. 221, 265, 328; Linz, Jahrb. f. wiss. Bot., 1896, Bd. xxix, p. 265. Cf. also 

 Sects. 70, 82. 



2 On the solution of starch by diastase, &c., cf. Schleichert, 1. c., p. 51 ; A. Meyer, 1. c., pp. 96, 

 227 ; Griiss, 1. c., and Beitr. z. Bot. von Ftinfstiick, 1895, Bd. I, p. 295. 



3 Beyerinck, 1. c., p. 268. Cf. also ref. in Ann. d. 1'Inst. Pasteur, 1895, T. ix, pp. 50, 121, 214. 

 1 Cf. Sects. 65, 82, 83, 84. On the destruction of wood by fungi, see R. Hartig, Lehrb. d. 



Baumkrankheiten, 2. Aufl., p. 51. Cf. also Green, 1. c., p. 93. 



