224 APPLIED BIOLOGY 



it is tumbled along. This is only one of many methods of 

 seed dispersal. The success of the common dandelion as 

 a weed depends in a large measure upon its efficient device 

 for scattering its seeds. Here, as in many other composites, 

 the upper end of the calyx forms a tuft of hairs which are 

 caught by the wind. In still other plants like the clematis 

 the style of the pistil becomes a feathery tail by which the seed 

 is wafted about. In the milkweed the little seed-stalk de- 

 velopes into a tuft of silky hairs so light that the slightest 

 breeze may carry the seeds miles away from the parent 

 plant. Plants like the elm, maple, ailanthus, and pine, also 

 depend upon the wind to scatter their seeds; but the simple 

 wing-like outgrowths from these seeds and fruits do not make 

 them very buoyant, and consequently they are not carried 

 far by the wind. In edible fruits like the wild blueberry, 

 pokeberry, currant, etc., the seeds are so hard that probably 

 they are not injured by being passed through the digestive 

 organs of the birds or other animals that feed upon the fruits, 

 and hence fruit-eating animals may serve as distributers of 

 hard seeds far from the locality where they grew. In such 

 cases as the black walnut, wild apple, osage-o range, etc., the 

 fruits, because of their rotund form, may roll some distance 

 from the parent tree. In some plants (e.g., witch hazel) 

 the seeds are inclosed in an explosive pod which when it 

 opens throws the seeds many feet away. The jewel- weed, 

 garden balsam, violet, and morning-glory also belong to this 

 type. In some plants the seeds or fruits develop hooks and 

 barbs which catch hold of the furs of passing animals or the 

 clothing of people and are thus widely scattered. Still others 

 have their seeds or fruits inclosed in waterproof husks or 

 envelopes so that they may be carried for miles by water, and 

 as in the case of the cocoanut fruit, probably thousands of 

 miles. It is probably in this way that the flora (collection 

 of plants) of isolated coral islands originated. Seeds are also 

 scattered in accidental ways, as for instance in the pellets 



