190 Fruits and Seeds. 



IV. 



1. In other cases the dispersion is mainly the 

 work of the seed itself. In some of the lower plants, 

 as, for instance, in many seaweeds, and in some 

 fresh-water plants allied to them, the spores* are 

 covered by vibratile hairs, and actually swim about 

 in the water, like microscopic animals, till they have 

 found a suitable spot on which to grow. Nay, so 

 much do the spores of some seaweeds resemble 

 animals, that they are provided with a red " eye- 

 spot" as it has been called, which, at any rate, 

 seems so far to deserve the name that it appears to 

 be sensitive to light. This mode of progression is, 

 however, only suitable to water plants. One group 

 of small, low-organized plants develops among the 

 spores a number of cells with spirally thickened 

 walls, which, by their contractility, are supposed 

 to disseminate the spores. 



2. In much more numerous cases, seeds are carried 

 by the wind. For this of course it is desirable that 

 they should be light. Sometimes this object is 

 attained by the character of the tissues themselves, 

 sometimes by the presence of empty spaces. Thus, 



* Speaking botanically, these are not true seeds, but rather moving 

 buds. 



