THE CONSTITUENTS OF PLANTS. 17 



tain quick growing biennials, as radishes, may produce 

 seed in one year, if removed from the soil after the root 

 is full grown, topped, and transplanted. 



"Perennials'^ are plants that live for more than two 

 years; timber-trees, fruit-trees, berries, grape-vines, etc., 

 are good examples, though perennials are not confined to 

 trees and shrubs; asparagus, a number of the clovers, 

 and various grasses, also belong to this group. 



Plant Development. — The development of the plant 

 after germination is not uniform ; the substances obtained 

 by the roots are greatest in the young plant, which is 

 always rich in nitrogen and ash elements. As the plant 

 grows, the proportion of food derived from the atmos- 

 phere through the action of the leaves steadily increases. 

 The wheat crop contains practically all of its nitrogen 

 and potash when in full bloom ; carbon increases as long 

 as the plant remains green. When the seeds begin to 

 form, the food gathered by the leaf and root is largely 

 transferred from the stem and leaf of the plant, and 

 concentrated in the seed. 



Cereals and grasses cut while the crop is green are 

 much richer in nutritive matter than when they are 

 allowed to ripen seed. In such crops as turnips, beets, 

 and potatoes, the development of root and leaf is the 

 same as in wheat; but at the completion of growth, food 

 is stored up or contained in the root, or tuber, and the 

 leaves die after the food in the plant has been largely 

 transferred. In trees, the plant-food gathered by the 

 root is concentrated by the end of summer in the pith 

 of the tender branches and in buds, and serves as food 

 for the new growths of another season. 



