56 
HOW CROPS GROW. 
Fig. 10 represents an extremely thin slice from the stem of a cabbage, 
magnified 230 diameters. The united walls of two cells are seen in see- 
tion at a, while at b an empty space is noticed. 
The outer coating, or wall, of the cell is cellulose. This 
substance is accordingly the skeleton or framework of the 
plant, and the material that gives tough- 
ness and solidity to its parts. Next to 
water it is the most abundant body in 
the vegetable world. 
All plants and all parts of all plants 
contain cellulose, but it is relatively most 
abundant in their stems and leaves. In 
seeds it forms a large portion of the husk, 
shell, or other outer coating, but in the 
interior of the seed it exists in small 
quantity. 
The fibers of cotton, (Fig. 11, a,) hemp, 
and flax, (Fig. 11, >,) and white cloth and 
unsized paper made from these materials, 
are nearly pure cellulose. 
The fibers of cotton, hemp, and flax, are simply 
long and thick-walled cells, the appearance of 
which, when highly magnified, is shown ih fig. 
11, where a represents the thinner, more soft, and collapsed cotton fiber, 
and % the thicker and more durable fiber of linen. 
