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 parti- 

 tions. 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 cham- 

 bers are known as "cells," and of them the whole plant is 

 built up. 



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 remov- 

 ing a stamen and placing it in a drop of 

 water under a cover glass. Each cell 

 (Fig. 1 ) is an oblong sac, with a deli- 

 cate 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 homoge- 

 neous fluid. This fluid, which in most cells is colorless, is called the 

 cell sap, and is composed mainly of water. Imbedded in the granular 

 6 



w 



"pr. 



FIG. 1. A single cell from a hair 

 on the stamen of the common 

 spiderwort (Tradescantia), 

 x 150. pr. protoplasm; w, cell 

 wall; n, nucleus. 



