110 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[ 25. 



however, the plastid remains in contact with but one end of the 

 developing grain ; hence the deposited layers are thicker and more 

 numerous on the end of the grain next the plastid, and the layers 

 become excentric (Fig. 67 A) ; the hilum thus necessarily becomes 

 removed further and further away from the plastid. 



It not uncommonly happens that compound starch-grains are to 

 be found. Spuriously compound grains are simply grains which 



have become adherent in con- 

 sequence of mutual pressure ; 

 they occur frequently in the 

 interior of the plastids (see 

 Fig. 52). The truly com- 

 pound grains (Fig. 67 BE) 

 stre formed in this way, 

 that, one plastid produces 

 simultaneously two or more 

 rudimentary starch -grains ; 

 as these increase in size, they 

 eventually come into con- 

 tact ; the further deposition 

 of starchy layers must ne- 

 cessarily be of such a kind 

 that they surround, not each 

 individual grain, but the ag- 

 gregate of adjacent grains ; 

 the young grains thus become 

 bound together by investing 

 layers, and a grain is pro- 

 duced w r hich has apparently 

 a number of hila. 



The form of the starch - 

 grains is characteristic in the 

 different plants in which 

 they occur ; thus those of the Potato (Fig. 67) are excentrically 

 oval; those of leguminous plants (Fig. 69), concentrically oval; 

 those of Rye, Wheat, and Barley, lenticular (Fig. 70). 



The distribution of starch throughout the different classes of 

 plants is a matter of considerable interest. Generally speaking, 

 it is confined to plants which possess chloroplastids, though a sub- 

 stance turning blue with iodine has been found to occur, diffused 

 throughout the protoplasm, in certain Schizomycetes (Clostridiam 



FIG. 67. Excentric starch-grains from the 

 tuber of a Potato ( x 800). A A fully developed 

 simple grain. JB E Compound grains; a b 

 young simple grains; c young compound grain. 

 (After Sachs.) 



