OF MICROSCOPIC OBJECTS. 119 
notice of polarizing objects would be incomplete without 
some allusion to them. A small piece of the Flustra 
avicularis, well prepared, is beautiful when examined in 
this manner. No selenite is needed, and yet the colours 
are truly gorgeous. It is often met with upon shells and 
zoophytes of a large size, and will well repay the trouble 
of searching for. Many of the Sertularidz are very beau- 
tiful with polarized light, and, indeed, no ramble upon the 
seaside need be fruitless in this direction. 
The different starches are quite a study in themselves, 
and are peculiarly connected with polarized light. They 
are found in the cellular tissue of almost every plant in 
small white grains, which vary considerably in size; that 
from the potato averages one-three-hundredth of an inch in 
diameter, and that from arrow-root about one-six-hundredth. 
To procure starch from any plant, the texture must first be 
broken up or ground coarsely; the mass of matter-must be 
then well washed in gently-flowing water, and, as all starch 
is totally insoluble in cold water, the grains are carried off 
by the current and deposited where this is stayed. In pro- 
curing it from the potato, as well as many other vegetables, 
it is but necessary to reduce the substance to a coarse pulp 
by the aid of a culinary grater; the pulp should then be 
well agitated in water, and allowed to rest a short time, 
when the starch will be found at the bottom, its lighter 
colour rendering it easily distinguishable from the pulp. It 
should, however, be washed through two or three waters to 
render it perfectly clean. 
These grains have no crystalline structure, but present a 
very peculiar appearance when examined with polarized 
light. Hach grain shows a dark cross whose lines meet at 
the point where it was attached to the plant, called the 
hilum. Round the grain also a series of lines is seen, as 
though it were put together in plates. This is more dis- 
tinctly visible in some kinds than others. 
As to the mounting of these starches there is little to be 
said. If the grains are laid upon the slide, and as small a 
