FUNGI. 



363 



One form of fungus has attracted much attention of late years, as 

 it has been represented to be the cause of the potato disease. From 

 my own observations I believe that an aphis invariably punctures the 

 leaf before the attack of the fungus. It is possible that the punctures 



FIG. 842. ^Ecidium violae, 

 nat. size and magnified. 



FIG. 843. jEcidium cydoniae, 

 nat. size and magnified. 



of the insect allow the zoospores of the fungus which have cilise to 

 penetrate into the interior structure of the leaf, whence the mycelium 

 spreads into every part of the texture of the plant. The fungus appears 

 as a white powder to the eye, but, when examined by a microscope, 

 the white patch proves to be a forest of little branching stems 

 surmounted by oval bodies. It was called by Berkeley Botrytis 

 infes taus, and now the genus is named Peronospora (fig. 844). 



\ 



FIG. 844. Potato Fungus, 

 magnified. 



FIG. 846. Polyactis, 

 magnified. 



FIG. 843. Lettuce Mould, 

 magnified. 



Parsnips are attacked by another species of Peronospora, namely 

 P. nivea; onions by a third, called P. Schleideniana ; peas by P. vicice, 

 lettuces by P. gangliformis (fig. 845), cabbages by P. parasitica, and 

 spinach by P. effusa. 



My Todece have sometimes been attacked by a microscopic fungus, 

 the Polyactis (fig. 846). It is a beautiful object under the microscope. 



