CHAP, vi The Metabolic Processes 385 



the latter consists of carbohydrate alone. Starch, in his 

 opinion, is formed in the same way in the plastid. 



Schimper, in 1883, developed his view of the action of 

 the plastid in the process, and suggested that such proto- 

 plasmic layers are formed and immediately undergo de- 

 composition, starch being one of the resulting products. 

 This implies' that starch appears as a secretion product 

 of the plastid. Schimper's views on this subject were 

 endorsed by Eberdt in the paper already quoted. 



Meyer, in 1895, attributed the appearance of the grain 

 to a process of crystallization in the outer layer of the 

 plastid. 



In 1896 Salter investigated the process of deposition 

 with great completeness, using very delicate methods of 

 staining, which enabled him to differentiate the structures 

 more clearly. He found the successive layers of starch 

 are always quite distinct, and observed that they stain very 

 differently from the plastid. According to him the latter 

 secretes definite starch substance, and in the layer as 

 originally laid down there is no evidence of any transition 

 layer such as was suggested by Strasburger and by Noll. 

 The outermost layer of the grain has always the same 

 composition as the oldest part, from which it differs only 

 in relative density. Salter called the layer most newly 

 formed at any moment the rand. 



An appearance of lamination in the grain accompanies 

 its formation. This was known before the year 1860 and 

 was the subject of a theory of structure and growth of 

 starch grains formulated by Naegeli in 1858, a theory 

 formed under the influence of his well known views on the 

 thickening of organized vegetable structures by intussus- 

 ception. He said the appearance is due to the alternation 

 of watery and dense layers, which arise in consequence of 

 tensions evoked by the mode of deposition of the layers. 

 These tensions increase by unequal nutrition and lead to 



GREEN B b 



