188 THE AMEiltCAN MONTHLY rjun6 



form of the fungus has run its course, and the infested 

 leaves or other portions are killed by the fungus and have 

 fallen to the ground, the mycelium in their tissues con- 

 tinues to grow, and gives origin to numerous sexually 

 produced reproductive bodies called oospores from their 

 mode of origin ; also termed resting-spores because they 

 require to remain in a resting or passive condition for 

 some time before they are capable of germination. 



During the winter the leaves containing resting-spores 

 may decay and completely disappear, but the oospores re- 

 main unchanged on the soil until the following spring, 

 when they germinate and give origin to minute conidia 

 which are distributed by wind, and those that happen to 

 be deposited on the young leaves of a suitable host-plant 

 germinate at once, enter the tissues, and within a few 

 days give origin to the conidial form of reproduction 

 once more. 



The function of resting-spores is to enable the fungus 

 to tide over that period during which the host on which it 

 is parasitic is not in a condition of active vegetation. 



Following the Peronosporese in the sequence of evolu- 

 tion, we come to the enormous group of fungi, in the 

 broader sense known as the Ascomycetes; and through- 

 out the assemblage conidial, and what may be termed the 

 sexual methods of reproduction are present. However, 

 in the Erysipheae, one of the oldest sections of the As- 

 comycetes, the resting-spore phase is still the result of 

 a sexual act, whereas in the Sphseriacese and other sec- 

 tions, although the fruit producing resting-spores is mor- 

 phologically similar to that of the ErysiphesB, it is in re- 

 ality asexual in origin ; traces of the sexual organs are 

 present in various sections, but are functionally effete, 

 and in others have become quite rudimentary. 



Finally, in the most modern and highly differentiated 

 group of fungi, the Basidiomycetes, there is no vestige 

 remaining of the originally sexual mode of reproduction, 



