CHAP, vi The Metabolic Processes 387 



concern the supply of crystallizable material to the grains. 

 The mode of lamination hence depends on the various 

 influences which have affected their growth. A second 

 factor is a periodically recurring solution of the peripheral 

 layers, followed by a resumption of deposition. 



Salter followed with great care the course of develop- 

 ment of the grains of a large number of plants. He noted 

 the following stages : (i) the leucoplast with a starch grain 

 beginning to form in its interior ; (2) the origin of the 

 nucleus, or kern, inside the grain, followed in the case of 

 excentric grains by an aggregation of the substance of the 

 plastid to one side ; (3) the appearance of a faintly-staining 

 zone round the kern, its marginal part gradually deepen- 

 ing in staining power and constituting the first lax lamina ; 

 (4) the succession of a number of laminae, capable of demon- 

 stration by staining. In excentric grains the more watery 

 laminae gradually fail to be recognizable the whole way 

 round the kern, causing the grain to become increasingly 

 excentric. Subsequent differentiation in these laminae then 

 causes the striation to be noticeable, but they gradually lose 

 their staining power from the kern outwards. The outer 

 layer (r and) generally fails to stain, but appears structureless, 

 and never shows lamination when young. When stains 

 affect it, it always behaves like the dense laminae. Salter 

 held that it always possesses a potential lamination, often 

 containing several layers that later show themselves to be 

 lax or watery. All the laminae are of different density in 

 different parts, but they only become visible as they are 

 covered by new depositions. 



Allusion has been made incidentally to a suggestion 

 of A. Meyer that the grain is composed of crystallizable 

 material. This view was originally advanced by Famintzin 

 in 1869, when he compared starch grains to sphere 

 crystals of calcium carbonate. It was more fully ex- 

 pounded by Schhnper in his paper of 1881 ; he called 



Bb 2 



