CHAP, vi The Metabolic Processes 381 



taining that in this process also, specially differentiated cor- 

 puscles or plastids are concerned. He found that in all 

 parts of a green plant in which starch is being deposited, 

 whether for longer or shorter periods, the grains in process 

 of development are associated with peculiar protoplasmic 

 bodies to which he gave the name starch-forming corpuscles, 

 and that those which occur in the non-green parts are 

 analogous to, if not identical with, the chlorophyll bodies. 

 Indeed the presumption of identity is very great, inasmuch 

 as the former can become green under favourable con- 

 ditions of illumination. Schimper's researches threw a flood 

 of light upon the details of the development of the starch 

 grain in or by the corpuscle, and thus opened the way to 

 more detailed researches into its structure. He also ascer- 

 tained that the vigour of plastids in different situations 

 is not quite the same, for while those of the bundle-sheaths 

 of the leaves of Tradescantia and those in the cortex of 

 its stem can form starch from the stores of carbohydrate 

 in the plant, thus confirming Boehm, the plastids of its 

 leaf mesophyll can only produce it from atmospheric carbon 

 dioxide. Confirmatory work on this point was published 

 about the same time by Dehnecke. 



Schimper said not only that starch grains are always 

 formed by the activity of what we now call a plastid, but 

 also that they arise in its interior. The grains with concentric 

 striation remain always inside it, but those whose markings 

 are excentric break through its substance and, protruding, 

 remain in contact with it on one side only. The plastid 

 absorbs, and is nourished by, the sugar, and subsequently 

 secretes the starch. 



Schimper's views were not at once accepted by all 

 botanists, though they met with a very cordial reception 

 in most quarters. Later inquiries have shown them to be 

 in the main correct, though certain exceptions to the pro- 

 cess he described have come to light. To these we shall 



