180 DIVISION II.—COURSE OF DEVELOPMENT OF FUNGI. 
single spores (or perhaps several successively) are abjointed. The spores are narrowly 
fusiform in shape, like the secondary sporidia of the promycelium, and it may be 
assumed, though it has not been observed, that their mode of germination is the 
same. They are formed on the mycelium before the resting-spores, and appear to 
the naked eye as a slight sprinkling of flour or mould on the spot which is attacked 
in the leaf. 
The most remarkable case of this kind was observed by Woronin in Tuburcinia ' 
Trientalis, The resting-spores of this Fungus germinate in late autumn. The 
mycelial primordia produced from the secondary sporidia penetrate into the young 
subterranean shoots of Trientalis destined to pass the winter, and develope a mycelium 
which also hibernates in their parenchyma. Next spring the mycelium spreads 
through the whole of the shoot as it unfolds, and at first forms gonidia on the under 
side of its leaves and afterwards the cluster of resting-spores, but more in the 
stem than in the leaves. The gonidiophores are branches of the intercellular 
mycelium and come out to the air through the stomata and lateral walls of the cells of 
the epidermis, covering the whole of the surface of the leaf with a white down. 
They are unbranched and subulate in form, and from the apex of each several 
spores (gonidia) are successively abjointed one after another, which are pear-shaped 
and not fusiform like the sporidia of the promycelium. Germ-tubes are put forth 
by the gonidia on the moist surface of a leaf of Trientalis and penetrate into it, and 
develope mycelia which are confined to small spots in the leaf, where they form clusters 
of resting-spores but not gonidia. 
Section LVIII. According to the above well-ascertained facts the course of 
development in the Ustilagineae (in species of Entyloma, in Ustilago Carbo, and Uro- 
cystis occulta), where the process is the simplest, appears to be, that the resting- 
spore produces a promycelium, and the promycelium the conjugating pairs, and the 
ınycelial primordia which proceed from them enter and develope in the host-plant 
and produce fresh resting-spores. The first complication is caused by the production 
of mycelial primordia, not directly from the conjugating pairs, but from secondary 
sporidia proceeding from them, as happens almost invariably in some species of 
Entyloma and in Tuburcinia Trientalis. Then comes in Entyloma Ranunculi, 
E. serotinum, and in Tuburcinia Trientalis the interpolation of gonidia which are 
formed on the endophytic mycelium and can produce similar mycelia. If we regard 
the resting-spores as carpospores in the sense. of section XXXIV, a point which will 
be discussed further on, the secondary sforzdia must be termed gonidia which have 
been interpolated in the course of the development. Lastly, a mycelium can also 
be produced on any dead substance which yields suitable nourishment and gonidia 
on the mycelium, and it may at least be assumed that the gonédia are capable of 
reproducing a mycelium forming carpospores. I have purposely avoided the general 
use of the word gonidium in the preceding pages, though it will have to be used from 
this time, in order to show by one example how the same object may and must have 
different names when considered from different points of view and in different 
connections. 
The facts that have been certainly ascertained are only these: that the species, 
whose course of development has been really followed throughout, Ustilago Carbo, 
-D. destruens, Tilletia, Tuburcinia Trientalis, Entyloma and Urocystis occulta, all show 
