V 



f 



1902] THE STRUCTURE OF THE STARCH GRAIN 347 



composition. A possible explanation of this phenomenon may 

 be that in the air bubble the violet rays, owing to their length 

 and velocity, completely overshadow the red rays ; whereas in 

 the starch grain the layers containing other substances offer a 

 resistance to and refract the violet rays and leave the red only in 

 view. As a result of this physical examination of the grain we 

 observe that the successive layers differ in density, and that these 

 correspond to the '* water-poor " and ** water-rich " lamellae 

 described by Nageli (16). 



We further find in some of the potato starch grains that at the 

 periphery of the point of origin of growth, as well as upon the 

 inside of one or more of the layers corresponding to it, there is 

 a dark line much resembling the peripheral layer of the grain 

 {fig- 3)' This probably led Dippel (22), Strasburger (23), and 

 Krabbe (24) , to consider that the lamellae did not differ in char- 

 acter, but that this appearance of lamellation was due to lines of 

 contact, as already stated. Krabbe in the chapter dealing on the 

 **SpiraIstreifung der Bastfastern '' further distinguishes between 

 *'Grenzflachen" and ''Contactflachen.'* He says: *'Schichten mit 

 derselben Streifung, jedoch mit verschiedener Steilheit derselben, 

 vorliegen, da wird ihre gegenseitige Abgrenzung dadurch noch 



w 



deutlicher, das die Grenzflachen der Spiralbander in der Con- 

 tactflache der Schichten nicht immer aufeinander Stossen." 



A further evidence that there is a marked difference in the lay- 

 ers of the grain is the effect produced by staining reagents {figs. 

 ^Qyjo)' On treating starch grains with weak aqueous solutions of 

 safranin and gentian-violet/ it is observed that certain parts of the 

 grain take up these stains more readily than others. The gen- 

 tian violet stain is more pronounced in its effect upon the potato 

 starch grain {fig- 3 5), it being held by the point of origin of 

 growth and the lamellae alternating with it. Safranin, on the 

 other hand, is a better differential stain for wheat starch grains 



[fig^ 



of the lamellae (usually not 



more than three or four of them being affected) and in numer- 



*The method used by the author consisted simply in treating the freshly isolated 

 starch grains, or the commercial starches, with weak aniline dye solutions and allow- 

 ing them to dry at an ordinary room temperature. 



