180 LECTURE X. 



although the exact mode of their formation in seeds has not 

 been investigated, it may be assumed that it is the same as 

 in other parts of the plant. Schimper has observed that the 

 formation of starch-grains is commonly effected, in parts of 

 plants not exposed to light, by certain specialised portions of 

 the protoplasm. which are termed starch-forming corpuscles or 

 amyloplasts. These corpuscles closely resemble the chloro- 

 phyll-corpuscles, though of course they contain no chloro- 

 phyll ; in some cases, in fact, an actual conversion of an 

 amyloplast into a chlorophyll-corpuscle, under the influence 

 of light, has been observed. In both cases, if we accept the 

 view of Strasburger, the starch formed is a product of the 

 C decomposition of protoplasm; the difference in function be- 

 tween chlorophyll-corpuscle and amyloplast is then this, that 

 in the former the synthetic processes begin with such simple 

 , substances as carbon dioxide, water, and salts, and are 

 I effected under the influence of light, whereas in the latter they 

 begin with tolerably complex substances (e.g. asparagin and 

 glucose), and in this case the influence of light is not essential. 

 Strasburger has found that in certain cases (macrospores 

 of Marsilia, cells of medullary rays of Pinus sylvestris) the 

 starch-grains are formed in the general protoplasm of the 

 cell. At their first appearance the starch-grains are minute 

 bodies usually more or less spheroidal in form ; as they 

 increase in bulk they begin to present the stratified appear- 

 ance mentioned above. When the. grains are formed in the 



FIG. 26 (after Schimper). Group of amyloplasts, each bearing a starch-grain, 

 collected round the nucleus in a cell of the tuber of Phajus grandifolius 

 (Bletia Tankervillice). 



I 



