140 



PLANT BIOLOGY 



The peculiar flowers of the pea tribes are explained in 

 Figs. 187, [88. 



Spathe Flowers. — In many plants, very simple (often 

 naked) flowers are borne in dense, more or less fleshy 

 spikes, and the spike is inclosed in or attended by a leaf, 

 sometimes corolla-like, known as a spathe. The spike of 

 flowers is technically known as a spadix. This type of 

 flower is characteristic of the great arum family, which is 





Fig. 187. — Flowers of the 

 Common Bean, with one 

 flower opened (a) to show 

 the structure. 



Fig. 188.— Diagram of Alfalfa Flower 

 in Section : 



C, calyx, D, standard; W, wing; A", keel; T, sta- 

 men-tube; F, filament of tenth stamen; A", 

 stigma; Y, style; O, ovary; the dotted lines at 

 /." show position of stamen tube, when pushed 

 upward by insects. Enlarged. 



chiefly tropical. The commonest wild representatives in 

 the North are Jack-in-the-pulpit, or Indian turnip, and 

 skunk cabbage. In the former the flowers are all diclin- 

 ous and naked. In the skunk cabbage all the flowers are 

 perfect and have four sepals. The common calla is a 

 good example of this type of inflorescence. 



Compositous Flowers. — The head (anthodium) or so- 

 called "flower" of sunflower (Fig. 189), thistle, aster, 

 dandelion, daisy, chrysanthemum, goldenrod, is com- 

 posed of several or many little Jloivrrs, or florets. These 



