LEAVES, BUDS AND FLOWERS 87 



THE FLOWER 



138. The flower is the developed and expanded flower- 

 bud (131). Its office is to provide for the formation 

 of new plants of its kind (reproduction, 16). Some 

 plants, as the quack-grass (Agropyron repens), Canada 

 thistle (Cirsium arvense) and horseradish (Radicula), mul- 

 tiply freely in nature without the aid of flowers, and 

 nearly all plants may be multiplied in culture by other 

 means, but in most of the higher plants, the flower is 

 the natural organ of reproduction, and the only organ 

 devoted solely to this end. 



139. Effect of flowers. Flowers tend to exhaust 

 the plant, since they are formed from the food prepared 

 by the leaves. But since flower-buds are not usually 

 formed until the needs of growth are provided for (134), 

 the normal production of flowers does not injure the 

 plant. In certain cases, however, as in plants weakened 

 by recent transplanting or in cuttings (358), flower-buds 

 should be removed as soon as discovered, to prevent their 

 exhaustive influence. 



140. Parts of the flower. The complete flower is 

 composed of four different parts or organs. A knowl- 

 edge of these parts is of great importance to the botan- 

 ist in determining species, and also to the plant-breeder 

 who would practice cross-pollination (151, 440), hence 

 we need to consider them in detail. The cherry blossom, 

 of which a vertical section appears in Fig. 45, will serve 

 as our first example. 



141. The calyx. Beginning at the bottom, the part 

 marked C in the figure is called the calyx. This is green 

 in the normal cherry flower. In some plants, as the flax, 

 the calyx is composed of several distinct, more or less 



