Most of the smaller parasitic fungi (rusts, mildews, etc.) may be kept dry for any length of time, and on moistening with a weak solution of caustic potash will serve nearly as well as freshly gathered specimens for most purposes.
When it is desired to preserve as perfectly as possible the more delicate plant structures for future study, strong alcohol is the best and most convenient preserving agent. Except for loss of color it preserves nearly all plant tissues perfectly.
CHAPTER II.
THE CELL.
If we make a thin slice across the stem of a rapidly growing plant,—e.g. geranium, begonia, celery,—mount it in water, and examine it microscopically, it will be found to be made up of numerous cavities or chambers separated by delicate partitions. Often these cavities are of sufficient size to be visible to the naked eye, and examined with a hand lens the section appears like a piece of fine lace, each mesh being one of the chambers visible when more strongly magnified. These chambers are known as “cells,” and of them the whole plant is built up.
Fig. 1.—A single cell from a hair on the stamen of the common spiderwort (Tradescantia), × 150. pr. protoplasm; w, cell wall; n, nucleus.
In order to study the structure of the cell more exactly we will select such as may be examined without cutting them. A good example is furnished by the common spiderwort ([Fig. 1]). Attached to the base of the stamens ([Fig. 85], B) are delicate hairs composed of chains of cells, which may be examined alive by carefully removing a stamen and placing it in a drop of water under a cover glass. Each cell ([Fig. 1]) is an oblong sac, with a delicate colorless wall which chemical tests show to be composed of cellulose, a substance closely resembling starch. Within this sac, and forming a lining to it, is a thin layer of colorless matter containing many fine granules. Bands and threads of the same substance traverse the cavity of the cell, which is filled with a deep purple homogeneous fluid. This fluid, which in most cells is colorless, is called the cell sap, and is composed mainly of water. Imbedded in the granular lining of the sac is a roundish body (n), which itself has a definite membrane, and usually shows one or more roundish bodies within, besides an indistinctly granular appearance. This body is called the nucleus of the cell, and the small one within it, the nucleolus.
The membrane surrounding the cell is known as the cell wall, and in young plant cells is always composed of cellulose.
The granular substance lining the cell wall ([Fig. 1], pr.) is called “protoplasm,” and with the nucleus constitutes the living part of the cell. If sufficiently magnified, the granules within the protoplasm will be seen to be in active streaming motion. This movement, which is very evident here, is not often so conspicuous, but still may often be detected without difficulty.