114 



COLLEGE BOTANY 



maples (Fig. 80, c), ash and elms, in which the wings are ex- 

 pansions of the ovarian walls. Some other winged seeds are the 

 seeds of the milkweed, catalpa and pijie, in which the wings are 

 expansions of the seed coats. Some of the oommon forms with 

 floats are the dandelion, in which the calyx is developed into a 

 float, and the milkweed, in which the float is developed from the 



Fig. 82. — Devices for seed distribution. 



seed coat. Some herbaceousi plants, when mature, break loose 

 at or near the surface of the gi'O'imd and are blown across: the 

 country, scattering their seed as they go (Fig. 82). 



(b) Seed Dispersal hy Anitnals. — Many seeds, such as burs, 

 beggar ticks, Spanish needles and sticktights, have hooks or other 

 devices by which they become attached to hair and fur of ani- 

 mals and are cai-ried for great distances. Seeds of some other 

 plantsi, such as those that are enclosed in fleshy fruits and 

 grasses, are eaten by animals and pass through the alimentary 



