OP 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 Sertularidae 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 1 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. Each grain shows a dark cross whose lines meet at 

 the point where it was attached to the plant, called the 

 hilum. Bound 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 



