VII] 



USTILAGINALES 



191 



the swollen region and ultimately fuse (fig. 157). Thus the mature brand- 

 spore in Ustilago Mayfts, as in other species, contains a single fusion nucleus. 

 Here, however, the nuclear association which usually takes place in the basidio- 

 spore is postponed till just before spore-formation. The parasitic mycelium 

 is therefore haploid instead of diploid as in the majority of cases. 



A very similar state of affairs has been described by I. Massee in 

 Ustilago Vaillantii which attacks various liliaceous plants, hibernating in 

 the bulb and forming spores in the anthers and ovary. In these organs 

 the hyphae produce numerous short branches divided by transverse septa 

 into cuboid cells which, like the cells of the vegetative mycelium, contain 

 each a single nucleus. Alternate septa disappear by deliquescence so that 

 binucleate segments are formed in each of which the two nuclei approach one 

 another and fuse to form the single nucleus of the spore. 



Germination in water takes place in the usual way; four-celled basidia 

 are produced and give rise to basidiospores. Among these there is no evidence 

 of conjugation. 



Ustilago antherarum forms its spores in the stamens of members of the 

 Caryophyllaceae ; pollen-formation is inhibited, and the anthers become filled 

 with fungal spores, which are distributed by the mechanism prepared for the 

 dispersal of the pollen. Germination takes place in dung decoction with 

 great readiness, the tubes being put out in three or four hours. Harper has 

 observed that when the spore nucleus undergoes mitosis one of the daughter 

 nuclei remains in the spore while the other passes into the basidium (fig. 1 580). 

 Here it divides, the two resultant daughter nuclei are separated by a wall, the 

 nucleus remote from the spore divides again and a second wall is formed. 

 Thus the three-celled basidium characteristic of this species is constituted. 



Fig. 157. Ustilago Maydis; a. uninucleate cells 

 before spore-f< .rmation ; b. conjugation; c. young, 

 uninucleate brand-spores ; after Rawitscher. 



Fig. 158. Ustilago antherarum 

 Fr ; a. germinati"n of brand- 

 spore; b. conjugation; after 

 Harper. 



