^226 BOTANICAL MICROTECHNIQUE, 



^distinct stratification, which is certainly due to varying water- 

 content. This may be shown by examining moist and dry 

 starch-grains in Canada balsam or the like (cf. 2g?k and 

 Zimmermann I, 87). The silvering described in 2Q7n may 

 also be carried out on starch-grains, as Correns (III, 331) 

 has shown. It is best done by drying at 50 C. starch-grains 



FIG. 53. I, starch-grain from the rhizome of Canna indica (x 300) ; II, the same, from 

 the seed of Beta vulgaris (X 500) ; III, the same, from the scale-leaves of Lathraa 

 squamaria (X 150) ; IV, endosperm-cell of ZeaMays\ V, starch-grains from the latex 

 of Euphorbia splendent (X 150); VI, the same, from the Sarsaparilla root (X 250). 



obtained by scraping and cleaned by washing and decanting. 

 When dry, the grains are covered with a few drops of a 5$ 

 solution of silver nitrate, then a large quanity of a 10$ solu- 

 tion of common salt is added, and the whole is exposed to 

 "bright light until the reduction is completed. The grains 

 .are finally dried again on the slide and mounted in Canada 

 balsam. There are then seen many granules of silver de- 

 posited in the more strongly swelling layers of most of the 

 larger grains. 



402. In polarized light starch-grains give a characteristic 

 figure, like that of sphaerocrystals ; but the orientation of 

 the optical axes is opposite to that of the sphaerites of inulin, 

 for example. In excentrically formed starch-grains, the 

 middle of the black cross is also excentric and always corre- 

 sponds with the organic centre of the grain. 



