24 Depletion of Endosperm of Hordeum vulgare. 



former may be as great or even greater than that of the scutellum 

 in the early stages of germination, even if its specific enzymic in- 

 tensity is very much less. 



There is another probable function of the " aleurone-layer " which 

 may indirectly be of great value to the seed. These cells, which 

 undoubtedly contain living elements, constitute the outermost peri- 

 pheral layer of an otherwise dead endosperm, which, were it not for 

 this protective sheathing of living cells, would be much more liable 

 to the attacks of any of the micro-organisms of the soil which suc- 

 ceeded in penetrating the seed-envelopes. It is a noteworthy fact 

 that the " aleuronic " cells are much more fully developed over 

 those parts of the seed which may be regarded as devoid of life, and 

 become very much more attenuated where they come into proximity 

 with the embryo whose cells, owing to their activity, do not require 

 an equal amount of protection. In the case of barley the threefold 

 layer of " aleurone-cells " lying within the pericarp and testa con- 

 stitutes a triple line of defence, which must be of some value in 

 protecting the amyliferous cells against the hordes of external 

 organisms when the grain is placed under the natural conditions 

 suitable for germination. 



We must express our great thanks to Mr. W. T. Thiselton Dyer 

 and Dr. D. H. Scott for the opportunities they have afforded us for 

 carrying out this research at the Jodrell Laboratory. 



Addendum. 



Since writing the above we have for the first time seen the full 

 and expanded account which Puriewitsch has given of his work in 

 Pringsheim's Jahrbuch,' vol. 31, 1897, p. 1. 



His observations on the self-depletion of the endosperm of the 

 Graminece take account only of the erosion and dissolution of the 

 reserve starch. He does not call attention to the equally im- 

 portant and necessary antecedent phenomena of cytohydrolysis, 

 which admit of a determination of the " aleuronic " or peripheral 

 origin of the autonomous changes and their mode of progression in 

 the endosperm. Puriewitsch, in fact, regards every cell of the 

 endosperm as capable of functioning as a depletive agent, whereas 

 our own work points strongly to the conclusion that when an endo- 

 sperm is deprived of its embryo the subsequent chemical changes 

 within it are initiated by the " aleurone-layer " only. 



It is correctly stated that such action commences near the scutellar 

 surface, and extends peripherally under the " aleurone-layer " ; but 

 the author explains this by the observations of Brown and Morris, 

 and Griiss,* that the proximal half of the endosperm contains more 



* The recent experiments of Griiss iu this direction were made on maize, not or 

 barley, 



