1899] MICROSCOPICAL JOURNAL. lSl 



tinct species, each having its own generic and specific 

 name. 



The special function of the conidial form of reproduc- 

 tion is to enable the fungus to extend its geographical 

 range ; as already stated, the conidia are exceedingly 

 minute, are produced in immense numbers, and in rapid 

 succession during that period of time when the host-plant 

 is in full foliage and active growth; are readily dissem- 

 inated by wind, rain, insects, birds, and other agents, and 

 are capable of germination the moment they are mature ; 

 consequently those that happen to alight on the foliage 

 of a suitable host-plant enter its tissues, and within a few 

 days form a new centre of disease from which conidia are 

 liberated to continue the extension of the species. 



As a rule parasitic fungi are only capable of growing 

 on host-plants that are allied to each other; hence from 

 the above account it can be readily understood how rapid- 

 ly it is possible for a fungus epidemic to spread, more 

 especially where numerous plants of the same species are 

 growing in close proximity, as is the case with most cul- 

 tivated crops. All fungus epidemics are due to the rapid 

 spread of the conidial form of the fungus. 



It is important that the significance of the conidial 

 form of reproduction should be clearly understood, for al- 

 though evolved very early after fungi passed from their 

 primordial aquatic home and took possession of the dry 

 land, and in the earliest forms to be considered as subor- 

 dinate to the older sexual form of reproduction, never- 

 theless the acquisition of a second mode of reproduction 

 proved to be a step in the right direction, and has con- 

 tinued to become more and more highly evolved, until 

 finally in the highest and newest types of fungal evolu- 

 tion we find the conidial mode of reproduction alone re- 

 maining, the sexual form of fruit having been complete- 

 ly arrested. 



Now returning to the Peronosporeas : after the conidial 



