20 



MICROSCOPIC PLANTS. 



[CHAP. 



it speedily ramifies in different directions, and bears 

 fruit at the tips of the branches, as at e, e ; these fruits 



are termed simple 

 spores, or conidia, 

 because from their 

 smallness they are 

 dust - like. It is 

 quite possible they 

 may be an early 

 state of the vesicles 

 which contain the 

 zoospores, as seen 

 Fig. 21. at /, g. However 



this may be, they 



are commonly arrested in growth while still small, 

 and they germinate in an exactly similar manner 

 with the zoospores themselves, and may be con- 

 sidered somewhat analogous with seeds. The Po- 

 tato fungus has another method of reproducing 

 itself in the 'swarm spores,' as shown at f, g. 

 These are so called because, on the application 

 of moisture (as supplied by rain or dew, or when 

 applied artificially), the vesicles set free a swarm of 

 from six to fifteen or sixteen other bodies known as 

 ' zoospores,' so named because they are furnished with 

 two lash-like tails, and are capable of moving rapidly 

 about like animalcules. This rapid movement usually 

 lasts for about half an hour, and (like the dust-like 

 conidia, or ' simple spores,' before mentioned) the 

 swarm spores generally enter the breathing-pores of 

 the leaf, and there germinate. So potent, however, 

 are the contents of these bodies when set free, that 



