270 RESPIRATION, FERMENTATION AND DIGESTION 



daily evident in the aleurone layer of seeds of some grasses, al- 

 though found in epithelial cells of embryos of palms, in which re- 

 serve material is deposited in the seed in the form of thickenings 

 of the cellulose walls. It passes from the embryo to the endo- 

 sperm by dialysis. 



Cytase is formed by many parasitic plants which use this 

 means of dissolving the cellulose walls of the host plants and 

 thus gain access to the protoplasts. Lignified and suberized 

 membranes are not attacked, and changes in the membrane may 

 be an adaptive device by which a possible host avoids penetra- 

 tion by fungi and bacteria. 1 



343. Action of Cellulose Dissolving Enzymes. Germinate a num- 

 ber of seeds taken from the ordinaiy dried dates of commerce, 

 which will need about six weeks. Two weeks after germination 

 has begun, cut cross sections of the seed and embryo. Note the 

 structure of the epithelial cells of the absorbing organ formed 

 from the cotyledon. Stain with iodine. Note the condition of 

 the walls nearest the absorbing organ. Stain a fresh section 

 with chlor-zinc iodide and note the color reaction in the con- 

 tiguous and distal regions. Boil a fresh section in Fehling's 

 solution and note the presence of a reducing substance, probably 

 sugar in the region nearest the embryo. 



Follow the action of cytase on the membranes nearest the 

 aleurone layer, and the epithelial layer of the cotyledon in the 

 plants used in the last experiment. 



344. Digestion of Sugars. A large number of kinds of sugar 

 occur in the plant, and at the present time six different enzymes 

 have been discovered, each of which acts upon but one or few 

 forms of the carbohydrate. Invertase, which has the power of 

 inverting or converting cane-sugar into glucose and fructose is 

 the most important. It is found in all parts of the higher plants 

 including pollen grains, and is also formed by yeast, moulds and 



1 Newcombe, F. C. Cellulose enzymes. Annals of Botany. 13 : 49. 1898. 

 Kohnstamm, P. Amylolytische, glycosidespaltende, proteolytische, und cellulose- 

 losende Fermente in holzbewohnende Pilzen. Beih. Bot. Centralb. 10 : 90. 1901. 



