‘Formation of Teleutospores of Ustilaginee. 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 Sou 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 7ou in 
diameter the gelatinous zone is only from 4 to 6u 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 sporcs 
either continue their development independently, or, what 
is more probable, their spore-forming hyphze 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 hyphe. 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, ‘‘ Beitrage zur Morphol. und Physiol, 
der Pilze,” 5 reihe. 1882. 
F 
