GKASSES OF IOWA. 85 



•epithelium columnar cells is a secretory tissue, and that there 

 is no doubt that one of the special functions of these cells is 

 the secretion of enzymes. 



It was Sachs who first stated that the columnar epithelium 

 was an absorptive layer, and most wriiers agree that this is 

 one of its many functions, but Brown and Morris say that the 

 absorptive function is secondary in its importance. Accord- 

 ing to these writers, when they had removed the columnar epi- 

 thelium, the embryo developed when it was placed upon a cul- 

 ture medium containing a readily assimilable carbohydrate, such 

 as cane-sugar or dextrose, just as it would have done in its 

 unmutilated state, and when such a mutilated embryo is placed 

 upon a starch gelatin mixture it entirely lost its power of cor- 

 roding and dissolving starch granules. The secretion of dias- 

 tase appears to be increased by the presence of the small quan- 

 tity of acid, and its secretion is stimulated by the presence of 

 •digestible mat'^rial, " that the flow of amylohydrolytic enzyme 

 from the glandular cells of the scutellar epithelium might be 

 influenced by the presence of starch, either in the granular 

 form f r as soluble starch. ' ' Starch does not stimulate the epi- 

 thelium cells to increased secretion. It has been known for 

 some time that the cell-walls of the endosperm end of a date 

 seed become dissolved and is used for the nourishing of grow- 

 ing plantlets. This was shown very nicely by Sachs.* 



This has also been abundantly proven for other seeds in 

 which the reserve material is cellulose. Mr. J. R. Greene, 

 who made a glyceric e extract of the cotyledons of the date 

 seed, concluded that the glycerine extract contained a trace of 

 enzyme capable of converting cellulose into sugar. Brown and 

 Morris have shown that during the early stages of germination 

 the cell walls of the endosperm are disintegrated, and that the 

 disappearance of the cell walls always precedes the attack 

 upon the starch granules. That malt of barley contains an 

 enzyme, to which they have given the name of cytohydrolytic 

 as well as amylo-hydrolytic enzyme. The former when 

 slightly assimilated and allowed to act upon wheat or barley, 

 causes disintegration As no other malt extract was used it. is 

 evident that this ferment has a decided soluble action upon the 

 endosperm-cellulose of Bromus mollis, where the cell walls are 

 considerably thickened, and also on the cell walls of other 

 grass seeds. It is also interesting to note here that heating the 



*Bot. Zeit. 20: 242, 249. pi. 9. 1862. 



