286 USTILAGINEAE. 



retain their capacity for germination for years. In water they 

 germinate immediately, and produce a single (rarely two) promy- 

 celium consisting of four or five cells, from the ends or partition- 

 walls of which oblong conidia continue to be abjointed for about 

 two days. The cells of promycelia may become connected with 

 one another by lateral branchlets. Delicate germ-tubes are 

 given off by the promycelial cells, by the conidia, or by secondary 

 conidia. In nutritive solutions, on the other hand, the spores 

 germinate much more vigorously, the promycelium is stronger, 

 the conidia are continuously abjointed from little sterigmata, 

 and go on sprouting in a yeast-like manner till, on exhaustion of 

 the nutriment, they germinate to form vigorous mycelial filaments. 

 The fusion of the cells of promycelia never takes place in nutritive 

 solutions. 



The infection of oat-plants takes place on the soil by means of 

 the germ-tubes produced from the conidia, promycelia, or spores. 1 

 These infect the first leaf-sheath that one which on germination 

 emerges from the ruptured seed-coats as a whitish or yellowish- 

 green shining shoot, and continues to grow as a sharp-pointed 

 cylinder till, pierced by the first green leaf, it dries up. In 

 36 to 48 hours after infection, mycelial threads were found 

 to have pierced the epidermal walls, and to have branched freely 

 in the tissues. The mycelium grows from the leaf- sheath into 

 the first green leaf, passes straight through it into the second, 

 and so on till it reaches the haulm or stem. 2 The young 

 mycelium grows steadily onwards, and the plasma of older 

 hyphae passes over into it. In this way the fungus keeps 

 pace with the host-plant, exhibiting externally no symptom 

 of its presence till the flowers are reached, where the chlamydo- 

 spores are formed. 



Sterilization of seed-corn by Jensen's hot-water method is 

 strongly recommended. 3 In America, steeps containing potassium 

 sulphide, copper sulphate, or lime are also used. As preventive 

 against infection, late sowing is advisable. This is founded on 

 Brefeld's investigations, in which he found that oat-smut germin- 



1 Wolf, Der Brand des Getreides, 1874. 



2 According to Klihn, and in Brefeld's infections (Heft xi. , 1895), the majority 

 of the germinating conidia are said to penetrate into the young shoot-axis. 



""Treatment of Smuts of Oats and Wheat," U.S. Depart mint of Agriculture, 

 Farmers' Bulletin No. 5, 1892; "Grain-smuts and their prevention," Yearbook 

 of U.X. l>'i>t. of Aijric'nlture, 1894. 



