MOEPHOLOGY OF THE BARLEY GEAIIST. 15 



of a ripe barley grain treated with. MiHon's solution presents a strongly 

 colored band just inside the aleurone layer and completely sur- 

 rounding the rest of the endosperm, showing the relatively high 

 proteid and low carbohydrate content of this region. The cell 

 contents, therefore, are obviously not identical with those beneath. 



It is but reasonable to suppose that these young and loosely filled 

 cells would be more easily broken down and that diastase, acting 

 from the proximal end of the grain, even if distributed equally over 

 the surface of the endosperm, would advance most rapidly along this 

 area of least resistance. A strong point against the aleurone theory 

 of digestion is the fact that the cells of the endosperm fii'st affected 

 are those next to the scutellum, as shown in Plate IV. If the aleurone 

 layer is active, why should not this take place uniformly in those 

 cells lying directly beneath that layer? Sections made through 

 grains geraiinated at high temperatures show the proximal end of 

 the endosperm to be in complete solution, while the ceUs next to the 

 aleurone layer toward the distal end of the grain are entirely un- 

 affected. Tliis can not be due to a lack of water, for water can be 

 sho\\^l to pass readily thi-ough the walls of all parts of the grain. 

 One or two authors have attempted to ascribe this condition to a 

 certain inexplicable stimulus which proceeds from the growing 

 plantlet and passes through the connected plasma of the aleurone 

 ceUs, inciting them to successive action. Such theory fails to explain 

 why the movement advances much more rapidly along the furrow 

 than elsewhere. The cells in this region are for the most part dead 

 tissue and would be incapable of aiding the aleurone layer or of car- 

 rying any stimulus. However, since the region of the furrow con- 

 tains the conducting tissue during the development of the grain and 

 since it leads past the scutellum, it is readily seen that it could be still 

 instrumental in carrying secretions from that source, although inca- 

 pable of conveying stimuli. 



A mf>re plausible defense of the theory of aleurone secretion has 

 been advanced in the statement that the enzyms are able to work only 

 when the j)ro<[u(;ts of their conversion are removed, and that the 

 scutellum as an a})sorbing organ is responsible for the fact that the 

 action comnienc<'s adjacent to it and can not proceed elsewhere, 

 except as tlie ]>rof,ess of removal becomes (vffcctivci. This thf^ory is 

 not hoi'iic out \)y observations, i.'i thai the lack of a m(^ilIls of removal 

 would not prev<'nt the prcliinitiatv stages of dissolution from taking 

 place at all [joints in contact with the aletn-one layer. No such ('ffect 

 occurs. Moccovci-, the pcfccnlage of maltose necessary t-o tlie in- 

 hibition of diustatic action is yrvy high, c<'rta,inly not. less than .'>() 

 per c<'nt. That tfiis percent ag<' is s<'ldoni rea,c,h('(| is shown hy th(^ 

 iiu;{ that the c<'ll-. fiisl !i(:l<'d upon while in ;i partial stiilc of conviM*- 

 sion j)ass on to the point of coniplctc dissohil ion, (•\<'n llioiigh Ihcy 



