2?6 DOWNY MILDEW OF MAIZE. 



before the rest of the crop is ready for harvest. Raciborski 

 describes the maize fields in Central Java as having thousands 

 of such diseased plants, the disease being of epidemic intensity. 

 At Pusa, so far, the cases have been few, but the progress of the 

 disease will be watched with some anxiety as the crop is an 

 extremely important one in Bihar and hitherto remarkably free from 

 fungus diseases of any kind. 



The cause is a fungus, named Pero)bos r pora Maydis by Raci- 

 borski. It is visible on cursory examination in the form of white 

 downy or woolly patches on both surfaces of the chlorotic streaks 

 on the leaves. These compose the fruiting or sporiferous stage of 

 the fungus, the main body of which occurs as threads or hyphse 

 within the tissues of the maize plant. 



These internal hyphse are large, unseptate and pursue a tortuous 

 course between the cells of the leaf mesophyll. Lateral swellings 

 indent, and perhaps penetrate, the cell walls, acting probably as 

 haustoria. When fructification is about to begin, hyphse collect 

 in the sub-stomatal air-spaces and from them small clusters of coni- 

 diophores arise through the stomata, coming out on both surfaces 

 of the leaf. 



The conidiophores are very thick and rather short, being 

 usually about 20 to 25m in breadth and 150m long, the length, 

 however, varying considerably. They are usually unbranched at 

 the base, but fork two or three times near the tip, the end branches 

 being stout and provided each with two or more sterigmata (PI. IX, 

 Figs. 1 and 3). Each sterigma bears a single conidium, which is 

 spherical when young but broadly oval when mature. The conidia 

 fall off readily when ripe, leaving the conidiophores devoid of 

 spores. 



The conidia (PI. IX, Figs. 1 and 3) are hyaline, thin-walled, 

 not papillate or stalked and measure 28 to 45 by 16 to 22// in dia- 

 meter. They germinate readily in water and may be found germin- 

 ating in large numbers on infected leaves in the field. One or 

 two germ-tubes arise from any part of the spore, giving a sparingly 



