THE DISPERSAL OF SEEDS 71 
trees which grow to some height. The utility of this 
arrangement is not difficult to understand. If the winged 
seeds were borne by low growing plants, they would fall 
to the ground long before the wind could carry them any 
distance. 
There are other seeds which the wind helps to scatter 
and which are without appendages of any kind. The seeds 
of the Poppy, Violet, and Pansy, are shaken out through 
Fig. 57.—A, Section through head of dandelion. Fig. 58,—Seed of 
a, receptacle; b, seed. Clematis, showing 
B, Section through single seed. feathery plume. 
c, seed; d, elongated calyx tube; e, tuft of hairs. . 
little openings in the capsule, whilst those of the wall- 
flower fall off from the central plate as the siliqua opens ; 
these plants, in fact, sow their own seeds. 
Dispersal by Clinging to Animals. Many seeds 
and fruits possess hooks, or rough or sticky surfaces, which 
enable them to cling to animals as these brush past them. 
In the Piri-Piri, usually called “ Bid-a-bid,” the ovary is 
covered with hooked spines—the whole forming the burr 
by which the seed is distributed. 
Dispersal by Birds. Seeds that are dispersed by the 
wind or by clinging to animals are usually dry, whilst 
