336 ENZYMES 



not unlike the crypts of Lieberkiihn of the intestine. These 

 secretory glands of the maize, however, have no lumina. In 

 Phoenix dactylifera the secretory organ of the seed is the 

 rounded structure situated opposite the furrow. In Nepenthes 

 and other insectivorous plants special glands occur in appro- 

 priate places, e.g. in the lining membrane of the pitchers, or in 

 special tentacles, as in Drosera. 



The fruits of Rhamnus infectorius are much used for dyeing. 

 The pericarp contains a glucoside, xanthorhamnetin, which, on 

 hydrolysis, breaks up into glucose and rhamnetin, a yellow 

 compound. This hydrolysis is brought about in nature by an 

 enzyme which is contained in the parenchyma of the raphe of 

 the seed. To illustrate this, the following experiment may be 

 tried. 



An aqueous extract of the separated pericarp is made and 

 placed in a glass vessel, then into the solution is thrown the 

 raphe of a seed. A golden yellow precipitate comes down.* 



In other cases the enzyme and substrate are contained in 

 different cells of the same tissue, so that it is only necessary to 

 crush up the tissue, or to macerate it, in order to obtain the re- 

 action ; the bitter almond, containing emulsin and amygdalin, 

 may be given as an example. 



The enzyme-secreting cells of Zea and Phoenix have been 

 studied by Reed.f He finds that in the resting condition 

 these elements are crowded with granules of a protein nature, 

 which disappear as secretion begins. At the beginning of 

 secretion, the nucleus is poor in chromatin, but this material 

 increases in amount as germination proceeds, the nucleolus 

 becoming smaller and smaller. Finally, at the end of the 

 secretory activity, the protoplasm of the gland-cells breaks 

 down, and the products of its disintegration disappear from 

 view. 



It may be remarked that in the dried condition enzymes 

 may retain their characteristic power for a considerable time ; 

 thus White % found that the ferments — diastase, protease and 

 ereptase — of the resting fruits of wheat and barley retained 



* Ward and Dunlop : " Ann. Bot.," 1887, i, i. 



fKeed: id., 1904, 18, 267; see also Huie : " Q.J. M.S.," 1897, 39, 387; 

 1899, 42, 203. 



^: White: " Proc. Koy. Soc, Lond.," B., 1909, 81, 417. 



