1899J MICROSCOPICAL JOURNAL. "71 



lating a healthy plant under proper conditions. Fig. 4 

 is a section of leaf through an aecidium and figure 5 is an 

 sBcidiospore. 



To Professor De Bary we are most of all indebted for 

 knowledge of these fungi which he worked out from 1861 

 to 1864. The five spore stages are: the promycelial spore, 

 the spermof^onium, the sBcidiospore, the uredospore, and 

 the teleutospore. De Bary discovered heteroecism or 

 metoecism, by which is meant that the secidium is only a 

 stage or special form of fructification in the life-cycle of 

 certain groups of fungi. 



The first case of this cyclic development noted was 

 that of mildew of wheat, the fungus being called Puc- 

 cinia graminis. 



"The mycelium of the aecidium or 'cluster-cup' stage of 

 Uromyces pisi (De Bary) is perennial in the tissues of the 

 host; hence, when plants are once attacked they never 

 recover, but produce the fungus year by year. The 

 aecidiospores, produced in the 'cluster-cups,' are dispersed 

 by wind at maturity, and those that happen to alight on 

 a leaf of the common pea (Pisum sativum) germinate 

 within a few hours if the surface of the leaf is damp ; 

 the germ-tube bores through the epidermis, enters the 

 tissues of the leaf and there forms a mycelium. This 

 mycelium, or vegetative portion of the fungus, consists 

 of a net work of anastomosing and transparent tubes. 

 These tubes, containing protoplasm, are divided by septa 

 at rare intervals into elongated cells. The septa become 

 more frequent at the points where sori are formed, and, 

 in Uromyces pisi and other species producing spores of 

 that color, orange granules appear in the protoplasm. 



About fourteen days after infection, the mycelium 

 produces dense tufts of uredospores, which burst through 

 the epidermis at maturity, and are distributed by wind 

 and rain. Those uredospores that alight on pea-leaves 

 germinate quickly, enter the tissues of the leaf, and, in 



