REPRODUCTIVE ORGANS. 



113 



75. Dispersal by locomotion. — The common method of 

 locomotion is by means of movable hairs (cilia) developed 

 upon the reproductive body, which propel it through the 

 water (see Fig. 109). 



Swimming spores are 

 very common among ,^ \ < ^" ; 



the algae, and at least 

 one of the gametes 

 in algae, moss-plants, 

 and fern-plants has 

 the power of swim- 

 ming by means of 

 cilia. 



76. Dispersal by 

 water. — It is very 

 common for repro- 

 ductive bodies to be 

 transported by cur- 

 rents of water. The 

 spores of many water 

 plants of all groups, 

 not constructed for 

 locomotion, are thus 

 floated about. This 

 method of transfer is 

 also very common 

 among seeds. Many 

 seeds are buoyant, or 

 become so after soak- 

 ing in water, and 

 may be carried to 

 great distances by 



currents. For this reason the plants growing upon the 

 banks or flood-plains of streams may have come from a 

 wide area. Many seeds can even endure prolonged soak- 

 ing in sea-water, and then germinate. Darwin estimated 



Fig. 112. The upper figure to the left is an opening 

 pod of fireweed discharging its plumed Beeds. 

 The lower figure represents the seed-like fruits 

 of Clematis with their long tail-like plumes.— 



After Kkknkh. 



