IN TROD OCT I ON. 



5 



green by a substance known as chloroph\ll. These are con- 

 sequently known as chloroplasis or chlorophyll-bodies (figs. 

 3, 4). In other cells, particularly those for the storage of 

 food, they may develop into smaller, denser, flattened or 

 roundish, uncolored bodies, called leucoplasls (figs. 5, 6, 7). 

 These may act either as starch-accumulators, or in case 



- A- 



Fic 



Fig. 



Fig. 6. — P.^rt of the cell-contents of an inner cell of white potato. 2, nucleus; j, 

 starch-grains, each ha\-ing been formed by a leucoplast, /, which is still attached to 

 one side of the grain; k, crystalloid. Magnified abont 1000 diam. — After Zimmer- 

 niann. 



Fig. 7. — Leucoplasts in place in a young cell of a leaf of vanilla, /, leucoplasts; 2, 

 nucleus; e. an oil-former or elaioplast. The unshaded spaces surrounded by proto- 

 plasm are vacuoles. Magnified about 1000 diam. — After Wakker. 



of need, in young cells, may e\en be converted into chloro- 

 plasts. In other cells, particularly in highly colored parts, 

 the plastids may become of most diverse form and size, and 

 colored red or yellow, whence they are called chromoplasis 

 or color-bodies (figs. S, 9). 



9. Wall. — The cell-wall is formed by the protoplasm. 

 In green plants when first formed it consists chiefly of cell- 

 ulose, with which, as it grows older, various other substances 

 may be mi.xed. Some of these, such as pectin, are present 

 even in the young wall, and may increase with age; others 



