268 RESPIRATION, FERMENTATION AND DIGESTION 



and all parts of the shoot as well as in the lower forms of plants. 

 The other, diastase of secretion, is to be found chiefly in germi- 

 nating seeds and does not appear until after germinating is well 

 under way. 



Many theories have been advanced as to the chemical action 

 ensuing during hydrolysis of starch, the best supported of which 

 seems to be that of Brown and Morris x that starch is composed 

 of a number of dextrin groups, which are successively split off 

 and converted into maltose. During the process many substances 

 appear in the reactions. 



Diastase of secretion is most active at 50—55° C, and its ac- 

 tion on starch grains results in their irregular corrosion, giving 

 them a jagged outline during dissolution. It is formed most 

 abundantly in the epithelial layers of certain embryos, although 

 some of it is present in the aleurone layer, which contains mostly 

 diastase of translocation, and both are accompanied by cytase. 

 Diastase of translocation is most active at temperatures of 40- 

 50 C, and it attacks the layers of the 

 starch granule uniformly so that its out- 

 ward form is preserved until almost com- 

 pletely dissolved. 



340. Enzymatic Glands of Seeds. Secure 

 some sound seeds of barley, oats, rye, 

 wheat, corn or Arisaema or any arum 

 and soak for a few hours in water. Cut 

 Fig. 130. Section of por- thin cross sections through the seed in 

 tion of scutellum of barley suc h manne r that the scutellum, or the 

 showing the secreting epi- r .. , , , ... . 



(helium. After Greene. u PP er P art of the cotyledon will be sec- 

 tioned at right angles. Treat some of the 

 preparations with nuclear and others with cytoplasmic stains. 

 Note the character of the layer immediately underneath the testa, 

 and also the outer layer of the embryonic organ in contact with 



1 Green, J. R. Fermentation. P. 32. 1899. 



2 Krabbe. Untersuchungen ueber das Diastaseferment unter specieller Beruck- 

 sichtigung seiner Wirkung auf StSrkekorner innerhalb der Pflanze. Jahrb. Wiss. Bot. 

 20 : 520. 1890. 



