SMUT FUNGI— USTILAGINES 253 



that a change is taking place within. The swellings are 

 indication of spore - formation, which proceeds sometimes 

 centripetally, so that . those on the exterior are most com- 

 pletely developed, the circumference darkens, and an epispore 

 is formed. In Siihacdotheca part of the hyphae are concerned 

 in the production of the receptacle and columella, and part in 

 the origination of the spores. In some genera the production 

 of spores is centrifugal, and the peripheral spores are sterile. 

 In Sorosjoorium " the spore-forming hyphae from several con- 

 tiguous mycelial branches incline together and twist them- 

 selves into a ball, as happens in the formation of a Lichen 

 thallus. These convoluted and contorting spore-forming 

 hyphae, being gelatinous, soon become so entwined and en- 

 tangled that they cease to be individually recognisable ; to all 

 appearances they coalesce together in part, if not entirely, and 

 on the exterior of this gelatinous ball other hyphae are seen 

 encircling it. These latter also being gelatinous, soon lose 

 their individuality, although at times traces of their concentric 

 arrangement can be made out. Spore-formation takes place 

 only in the central gelatinous ball, in the middle of which it 

 commences by the central part darkening in colour and 

 becoming differentiated into spore-like bodies, which vary in 

 number from four to sixteen. Apparently these bodies again 

 subdivide, so that when the spores arrive at their maturity 

 the spore-balls contain sixty to a hundred or more spores. In 

 the young state the developing spores are polygonal from 

 mutual pressure ; subsequently the balls increase in size, and 

 the gelatinous zone swells also. When the spores assume 

 their dark brown colour the gelatinous zone begins to be ab- 

 sorbed, and entirely disappears when the spores are fully 

 matured. In a certain sense the spore formation is centri- 

 fugal, as it commences in the centre of the gelatinous ball, but 

 the peripheral spores are the oldest, having been pushed 

 outward by the formation of younger spores in the centre." ^ 



The spores of the Ustilagineae are practically teleuto- 

 spores, and are called such by some writers. They are com- 

 posed of two membranes — the outer, or exospore, the thicker 

 and dark coloured ; the inner, or endospore, thin and colourless. 



^ British Uredineae aiul Ustilagineae, by C. B. Plowright, London, 1889, p. 64. 



