CH. VIl] 



USTILAGI'NALES 



i8s 



The mature brand-spore is uninucleate, and is surrounded by a delicate 

 endospore and by an epispore which may be smooth or variously sculptured 

 and usually contains pigment, giving the spore a black, brown, or violet 

 colour. 



On germination the spore gives rise to a short tube, the promycelium or 

 basidium (fig. 147), into which its contents pass, the nucleus undergoing at 



h I \c \ /d 



Fig. 147. Ustilago Scabiosae Sow.; development of basidium; after Harper. 



least two divisions; the basidium in turn produces a number of uninucleate 

 sporidia or basidiospores. The basidium may be unicellular, giving rise to 

 a bunch of basidiospores at its apex (Tilletia (fig. \\%d)), or multicellular, 

 usually four-celled, producing one or 

 more basidiospores from each cell (Us- 

 tilago (fig. 147 e)). The nucleus of the 

 parent cell does not travel into the 

 basidiospore but divides, sending one 

 daughter nucleus into the spore, while 

 the other, remaining in the basidial cell, 

 may undergo further divisions so that 

 nuclei are provided for a number of 

 spores. 



Under suitable conditions the basi- 

 diospores are cut off in considerable 

 numbers. They may further multiply 

 by budding, giving rise to conidia, or 

 a, delicate mycelium may be formed 

 from which conidia are abstricted {Til- 

 letia). A supply of conidia is produced by these means in dung decoction 

 and other nutrient solutions, and no doubt in the damp, manured soil of the 



Fig. 148. Tilletia Tritici (Bjerk) Wint. ; a. 

 basidium thirty hours after germination of 

 brand-spore;^, after conjugation of basidio- 

 spores ; X 300 ; after Plowright. 



