18 PLANT-LIFE 



the water is exhausted, the cells constituting the threads 

 form spores, which, in the case of B. subtilis, are endo- 

 spores, being formed inside the cells. Only one spore 

 is formed per cell (Fig. 7, c), so spore-formation is not 

 for multiplication, but for a resting condition, in which 

 the organism can tide over unfavourable circumstances. 

 The spores possess astounding vitality; they are not 

 injured by being dried, and can endure adverse con- 

 ditions very long periods — until, indeed, they find a 

 suitable substratum in which they can germinate. 

 Having found a proper food solution, the spore-mem- 

 brane bursts, setting free the cell-contents, which 

 speedily resume the normal activities of a bacterium. 

 Such is the career of the Hay Bacillus, which may be 

 regarded as typical of its class. It will be remarked 

 that there is not the slightest trace of sex in these 

 organisms. 



But where are we to place the Bacteria in the genea- 

 logical tree of plant-life ? Their minuteness and sim- 

 plicity might lead a superficial observer to place them 

 among the first plants, to say that in them we surely 

 have the very beginnings of plant-life; but such an 

 observer would overlook weighty facts. In the first 

 place, the great majority of the Bacteria are parasites 

 or saprophytes, utterly dependent upon existing organic 

 matter for food; therefore they must benefit by the 

 activity of plants which can build up organic bodies 

 from inorganic materials. Again, their general antipathy 

 to light, and parasitism, indicate degradation rather 

 than the upward trend. We may surmise that the Bac- 

 teria have descended from minute motile plant forms, 

 which in one direction have given rise to the green plants 



