302 THE BASIDIOMYCETES 



by gelatinization of intercalary cells or of contiguous cell mem- 

 branes. The spores are joined in spore balls among species of 

 Tolvposporium, Testicularia, Thecophora, Tuburcinia, Doas- 

 sansia, and Urocystis. In Urocystis the outer cells are sterile, in 

 Testicularia the inner ones are sterile, and in Doassansia sterile 

 cells may occur both at the periphery and at the core of the spore 

 balls. 



Germination of spores. The spores of smuts may germinate 

 only after a period of dormancy or immediately after maturity. 

 In any event there are among them two types of germination, 

 which are the bases for separation into families. Among the 

 Ustilaginaceae the spores give rise to a septate basidium (promy- 

 celium), from each cell of which a series of sporidia or basidio- 

 spores may be produced laterally. Among the Tilletiaceae the 

 smut spore usually gives rise to a non-septate basidium bearing a 

 cluster of elongated primary sporidia at its tip. Buller regards 

 these primary sporidia as specialized sterigmata that in turn give 

 rise to true sporidia. 



Within these two types there are various modifications. For 

 example, laterally borne sporidia in Ustilago zeae or U. avenae 

 may repeatedly sprout in yeast-like fashion, and eventually the 

 buds, when brought in contact with host tissues, form an infec- 

 tion hypha. In U. bro7nivora on brome grasses, sporidia pro- 

 duced on the basidium do not sprout but form new germ tubes, 

 which in turn produce sporidia. In U. olivaceae on Carex, a 

 primary sporidium is formed in place of a basidium, and this 

 sporidium buds indefinitely. Thecophora defoiinans on various 

 legumes does not form a true basidium. In Ustilago niida on 

 barley and U. tritici on wheat the basidium is replaced by a much- 

 branched hypha, and sporidia are not formed. 



Modes of infection among smuts. From the classical re- 

 searches of Brefeld (1883, 1895) has come much of fundamental 

 importance on modes of infection. In these studies the following 

 types are distinguished: (1) Infection of seedlings, in which con- 

 ditions favor coincidental germination of the seed and the smut, 

 and seedlings are penetrated before they emerge from the soil. 

 This kind is typified by Tilletia tritici, causing bunt of wheat, and 

 Ustilago avenae, causing oat smut. (2) Infection of any embry- 

 onic tissues, resulting in local lesions in various organs, such as 



