450 DEVELOPMENT OF STARCH-GRAINS IN EUPHORBIACEJAE. 
of a dilute solution of chromic acid in order to render this struc- 
ture visible. This reagent swells the starch-grains; but the 
stratification is still indistinct, is hard to observe, and is roughly 
parallel to the outline of the grain, the hilum being seen as a 
line in the centre of the grain in the direction of its long axis. 
As regards their optical properties, these starch-grains are doubly 
refractive; they do not, however, give a black or white cross as 
other starch-grains. When the prisms of a polarizing-micro- 
scope are turned so as to give a black field of view, then in the 
centre of the starch-grain one sees a black line surrounded on 
both sides by white lines; and, similarly, when the prisms are 
turned so as to give a white field of view, a white line surrounded 
by black ones. We see that, in all respects, these starch-grains 
agree with ordinary starch-grains, since they are developed in 
the interior of a starch-forming corpuscle, and by its agency they 
are stratified and are doubly refractive. The hilum, which is 
that part of the starch-grain which is first formed, appears when 
the grains are swollen as a line, and the lines of stratification 
enclose this and are roughly parallel to the outline of the grain, 
thus affording a proof that the development proceeds as in the 
manner above described. 
From the abstracts given above from Crüger's paper, we see 
that, with the exception of the Euphorbiacez, he had discovered 
the existence of the starch-forming corpuscle, though he had not 
understood its meaning, since he regarded it, not as an active 
agent in the formation of starch, but as an intermediate sub- 
stance in its formation made by the protoplasm or chlorophyll- 
corpuscle. That he should not have seen this body in the 
laticiferous cell of Euphorbia is surprising; for it is plainly 
visible when latex from near the end of a growing shoot is ex- 
amined with a microscope ; the starch-grains lying in it are 
seen (fig. 3, a, b, c) enclosed in the starch-forming corpuscle. 
On treatment with water, the starch-forming corpuscle swells up 
(fig. 3, d). 
