EVOLUTION OF PARASITIC FUNGI. 107 



places, as in the crevices of the bark of the vine or in simihir 

 crevices on the trellis. 



The same is the case Avith the strawberry leaf-blight, the 

 raninlaria stage being the form Avhich produces the disease, 

 while the perfect form, the sphterella, is developed in the dead 

 spots of the leaf, probably late in the season, or during the 

 winter or in the spring. Even here it is not necessary for the 

 continuation of the fungus in the ramularia form, for there are 

 stromata or rudimentary sclerotia developed from the mycelium 

 on the diseased spots, Avhich live through the winter and are 

 able the following spring to develop a crop of the conidia while 

 the sclerotium is lying on the ground. Thus the disease is 

 started anew for the season without the intervention of the 

 sphaerella form, and this probably happens in a great majority 

 of cases, since the sphaerella stage is rarely collected. 



So with the leaf-spot of the pear and quince. The parasitism 

 is brought about by the imperfect form, the entomosporium, 

 which causes small broAvn spots on the leaves, of a nearly 

 circular outline, with darker minute elevated pustules containing 

 the conidia. These become ruptured in an irregular manner and 

 set free the insect-like conidia. On the fruit it causes irregular 

 blackish spots which check the growth of the fruit tissue at these 

 places and may cause it to crack. The perfect form of the fungus, 

 which Sorauer calls stigmatea, develops on the fallen leaves dur- 

 ing the winter and the following spring. But it is not necessary 

 as a means for bridging the fungus over the winter period, even 

 though the ascospores mature early enough in the spring for an 

 infection of the leaves from that source, since the entomospo- 

 rium spores also live through the winter on the fallen leaves, or 

 are developed in the pustules which have hibernated, and the 

 infection can take place from them as well. 



The leaf-blight of cotton has a similar history, the parasitism 

 arising from the imperfect form, or rather the conidial form, 

 being the one which appears on the living leaves, while the 

 spha?rella form develops on the dead fallen leaves. AVhether 

 the cercospora form of the cotton leaf-blight can live through 

 the winter has not been determined, but it is likely that it can. 



Besides a few instances in which the perfect forms are knOAvn, 

 there are a very great number of the imperfect forms which have 

 not been connected with a perfect form. It is true that the 



