Vegetal Evolution. 145 



is sufficient to transfer the organism from the one 

 kingdom to the other. Their fecundity is extra- 

 ordinary, for Colin calculates that a single bacterium 

 could in three days produce uncounted millions.* 



(b) Swarm-spores. — Many simple organised crypto- 

 gamic plants generate peculiar fertile and locomo- 

 tive asexual cells, called swarm-spores or oosphores, 

 virtually the egg-seeds of those plants. Sometimes 

 they mimic amoebae in their motions, but more fre- 

 quently, provided with minute vibratile cilia or strongly 

 developed flagella of their own protoplasm, they lash 

 the surrounding water and travel rapidly from place 

 to place. 



These cilia and flagella are indistinguishable from 

 similar structures in animals, only, instead of remain- 

 ing transitory films of jelly, they develop into clearly 

 defined organs of constant form. Thus, in man 

 (whose wind-pipe and bronchise they clothe with a 

 continuous layer), the vibratile cilia are simply pro- 

 longations of the cellular protoplasm, which, having 

 lost the faculty of changing form, yet preserve the 

 primordial function of movement. 



Swarm-spores avoid obstacles, advance and retire 

 at pleasure, and are sometimes fascinated and some- 

 times repelled by light. Sooner or later they anchor 

 themselves to a rock, become comatose, roots spring 



* Man's alimentary canal is thronged with bacteria which prepare 

 the food for its passage through the intestines into the blood vessels. 

 Some biologists thus facetiously ask if man is an individual or a colony 

 of individuals. 



K 



