392 The Physiology of Plants BOOK in 



in size, growing inwards as well as outwards, till the grains 

 could be seen as conspicuous masses embedded in the proto- 

 plasm, which in consequence of their development assumed 

 the appearance of a coarse network. The vacuole of the 

 cell became filled up by the continuous formation of aleurone 

 grains, till the cell was swollen up by its own deposits. 

 The growth of the grains in this way was accompanied 

 by gradual chemical change, which was evinced by their 

 behaviour towards solutions of neutral and alkaline salts. 



Rendle was consequently of opinion that the process of 

 aleurone grain formation is one of true secretion and not 

 as Pfeffer thought of mere mechanical precipitation. He 

 opposed Pfeffer's view that the formation is determined 

 in any way by the mineral matter, whose presence indeed 

 in the cell he was unable to detect when the formation of 

 the grain began. 



A third theory still more fully recalling the work of 

 Schimper was based by Van Tieghem on certain re- 

 searches conducted in 1886 by Werminski, and in 1888 

 by Wakker. Both these authors noticed that in the cells 

 of the endosperm of Ricinus the protoplasm at an early 

 stage exhibited the presence of several distinct vacuoles, 

 and later an aleurone grain was formed in each vacuole, 

 the latter appearing to be gradually filled with protein 

 substance as the seed ripened. Van Tieghem suggested 

 that the apparent vacuoles are really plastids, which, on 

 account of their watery content, he termed hydroplastids. 

 On this hypothesis aleurone grains like starch grains are 

 not formed from the cell protoplasm but by differentiated 

 plastids. 



Each of these three theories received support from sub- 

 sequent writers, and at the close of the century the question 

 remained unsettled. Liidtke, in 1890, working on Ricinus, 

 came to the conclusion that both crystalloid and globoid 

 originate in the cytoplasm, and that the vacuole has no 



