Formation of Teleutospores of Ustilaginee. 71 
of mutual compression by being flattened in one or more 
directions. In JU. caricis they are often flattened on one 
side, so as to be subhemispherical. In size they vary 
from 4u in U. hypodytes to 30u or more in Uvocystzs fischert. 
They may be simple or collected into spore-balls (Soro- 
sporium), in which case they appear, when seen separately, 
asin Z. hyalina, to be segments of a sphere, being convex 
externally, but internally more or less wedge-shaped. In 
Urocystis the spore-balls are surrounded by a variable 
number of barren spores or pseudospores, which are paler 
in colour, often almost hyaline ; these do not germinate. 
Hartsen * found that the spores of the U. maydis would 
not yield their colouring matter to any of the ordinary 
solver.ts, but that strong sulphuric and nitric acids de- 
colourized the epispore, rendering it more transparent 
without at once destroying it, so that the contour of the 
exterior remains unaffected. Although the spores some- 
times burst, yet by these reagents the structure of the 
epispore can be conveniently examined. In nitric acid 
the spores of the U. maydis swell up, and after a time 
they dissolve, giving off an odour of bitter almonds. Sul- 
phuric acid is the better reagent to employ in the exami- 
nation of the spores, as, although it decolourizes and renders 
the epispore transparent, yet it does not so rapidly 
destroy the latter. 
* Hartsen, ‘Compt. rendus ” (1874), pp. 441, 442. 
