14 



BULLETIN 183. U. S. DEPAETMENT OF AGEICULTUEE. 



Tangl ^ has shown that the thickened cell walls in the endosperm 

 of many seeds are provided with openings, so that the cell contents 

 are not isolated but in intimate contact. This is true of the aleurone 

 layer of barley, and the layer is in consequence more nearly a unit 

 than might be supposed. 



The accumulative importance of these and other facts has caused 

 many authors to assert that the aleurone cells have a very important 

 secretive function. The views of the individual experimenters who 

 are inclined to this opinion are too numerous to discuss separately. 

 The points of variance between them and the writers are few and 



turn largely on the 

 interpretation of 

 specific phenomena. 

 These differences 

 really center around 

 a single fact. When 

 the breaking down 

 of the starch endo- 

 sperm once com- 

 mences next to the 

 scutellum, it follows 

 rapidly through the 

 cells immediately 

 beneath the aleurone 

 layer. This point is 

 frankly admitted, 

 but is far from being 

 a proof of aleurone 

 activity. It has other 

 interpretations more 

 consistent with the general facts of germination. These cells adja- 

 cent to the aleurone layer are markedly different from those of the 

 rest of the endosperm. They are younger. The starch endosperm 

 is laid down and its cells filled in centrifugal order, so that its 

 outer areas are the latest in formation and the latest in starch infil- 

 tration. They are also less gorged with starch. A grain of barley 

 is not definitely limited in growth. In a way its growth is inde- 

 terminate, its development progressive until stopped by the act of 

 ripening, a stage in which the failure of the supply of food is a marked 

 factor. As may be seen in Plate III, the outer cells must from their 

 very nature be younger and less filled with starch, their walls less 

 desiccated, and their nuclei in a more nearly normal condition than 

 those of the more thoroughly matured storage cells. A cross section 



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Fig. :-;.— Section of piece of "brewers' grain," that is, of a barley grain 

 that has passed thi'ough both the malting and the mashing processes. 

 The aleurone layer remains unchanged. The cell contents are 

 slightly shrunken by heating m the mash tub. The starch endo- 

 sperm is fully depleted of its contents. 



1 Tangl, Eduard. Ueber offene Commnnicationen z.vischen den Zellen des Endosperms einiger Samen. 

 Jahrbucher fur Wissenschaftliche Botanik [Pringsheim], Bd. 12, Heft 2, p. 170-189, pi. 4-6 [18S0]. 



