Fornnation of Telctitospores of Ustilaginea. 65 



that when the spores arrive at their maturity the spore- 

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

 young state these developing spores are polygonal from 

 mutual pressure, and they are to be found in spore-balls 

 not more than 50/.< in diameter. In the subsequent de- 

 velopment of the spores the balls increase in size, and the 

 gelatinous zone swells also. When, however, the spores 

 assume their characteristic deep brown colour this gela- 

 tinous zone begins to be absorbed, having been utilized in 

 the development of the spores. In spore-balls of 70/j in 

 diameter the gelatinous zone is only from 4 to 6^ thick. It 

 entirely disappears when the spores have attained their 

 full maturity. In a certain sense it may be said that the 

 spore-formation is centrifugal, inasmuch as it commences 

 in the centre of the gelatinous ball ; but the peripheral 

 spores are as in Ustilago, the oldest, having been pushed 

 outward by the continued formation of the younger spores 

 in the centre of the mass. These externally placed spores 

 either continue their development independently, or, what 

 is more probable, their spore-forming hyphae have become 

 greatly elongated, but still remain in connection with the 

 host-plant (Plate V. Fig. 12). In Sorosporium, however, 

 certain solitary spores occur independent of those aggre- 

 gated into spore-balls. The development of these isolated 

 spores takes place in single hyphae. The end of the hypha 

 becomes gelatinized, swells up, and a spore is developed 

 inside. They are at first surrounded by the gelatinized 

 hyphae, which generally, however, disappear entirely by 

 the time the spores are mature. 



Tubercinia. — The spore-formation of Tubercinia has 

 been worked out by Woronin * in Tubercinia trientalis. 



* Woronin, " Beitrag. sur Kenntniss der Ustilagineen " (1882), pp. 4-16, 

 t. ii. figs. 3-10. De Bary and Woronin, " Beitriige zur Morphol. und Physiol, 

 der Pilze," 5 reihe. 1882. 



F 



