SPORES AND THEIR DEVELOPMENT 



301 



they arise from special hvphal branches that constitute a dense, 

 tangled mass within the host tissues. Each cell of this mass is 

 binucleate (dicaryotic), as was first pointed out by Dangeard in 

 1894. Those cells, destined to become chlamvdospores, enlarge, 

 their contents become densely granular, and their walls become 

 gelatinized. New walls that persist are laid down within the 

 gelatinized walls, and as a result of disappearance of the gelat- 



FiG. 116. Ustilago scabiosae. A to E. Stages in germination of chlamvdo- 

 spores, basidium formation, and production of sporidia, t)^pifving that in 

 Ustilaginiaceae. (Adapted from Harper.) 



inous outer layer the spores are separated from each other. Bv 

 the time the spores have reached mature size the two nuclei unite; 

 the new walls then thicken, and the characteristic uninucleate 

 (monocaryotic) smut spore has come into being. 



De Bary regarded smut spores as resting spores, since thev 

 fail to germinate immediately upon maturity. Plowright termed 

 them teleutospores (teliospores), a term earlier applied to the 

 spore that forms last in the annual cycle of rusts. On the basis of 

 the period of their formation and method of germination he re- 

 garded the smut spore as the homologue of the rust teliospore. 

 Brefeld early observed their method of formation and concluded 

 that they are chlamydospores. 



In certain genera, such as Ustilago, Tilletia, Sphacelotheca, 

 Cinctractia, and Entyloma, the spores form singly and are freed 



