128 
chrome ; they then by their combined pressure rupture the cuticle, and constitute 
the Uredo above mentioned. 
If a few fresh ripe spores be placed upon a drop of water on a glass slide, and 
kept in a damp atmosphere, they will, in three or four hours, germinate. This 
process is very interesting, and can easily be watched by anyone who cares to take 
the trouble to do so. In from two to four hours, most of the spores will have pro- 
truded two germ tubes from the middle of their length. These tubes come through 
two circular openings in the thick wall of the spore; in from five to six hours, the 
germ-tubes will be twice or thrice the length of the spore, and in them will be seen 
yellow granules from the interior of the spore. Asa rule, only one of these germ- 
tubes continues its growth, which it does so rapidly that in from twenty to twenty- 
four hours it has become many times the length of the spore. During this time 
nearly the whole of the yellow endochrome (contents of the cell) has passed from 
the interior of the spore, and from the abortive tube, to the extremity of the grow- 
ing one. This tube has not only grown longer, but has taken a variable number 
of spiral twists like a corkscrew. It now, at the end farthest from the spore, gives 
off a number of irregular branches at a more or less rectangular direction. The 
lower end of the tube is now cut off by a septum from the empty spore-case.* If 
this germination has taken place upon the cuticle of the wheat plant (or any other 
grass upon which the Uredo is parasitic) one or more of the branches gains an 
entrance into the interior of the leaf through the stomata. Once inside the leaf, 
the mycelium is in its proper soil and luxuriates, as before said, by ramifying be- 
tween the cells of the host-plant, and, in due course, produces Uredo-spores. But 
the host-plant does not live for ever; on the contrary, many of the grasses die 
down in winter, and although Uredo-spores have, under favourable circumstances, 
been known to retain their germinative power + for some time, yet they lose it if 
kept dry for one or two months at most. Probably in a state of nature they would 
germinate soon after they were ripe, and so become effete. How, then, is it that 
this rust re-appears year after year? 
Seconp Stace: Restinc-sPoRE—Pvucornia oR MILpeEw (Fic. 2), 
Towards the end of summer, the mycelium, which has been continuously 
developing Uredo-spores, produces a resting-spore—or a body which has the faculty 
of lying dormant throughout the winter and germinating in spring. These resting- 
spores, or ‘‘teleutospores,” constitute the Puccinia graminis, or wheat mildew 
proper. They are produced in a similar manner to the Uredo-spores, but are very 
different in structure. Each teleutospore is club-shaped, and divided transversely 
into two compartments by aseptum. In colour, when seen by transmitted light, 
they are a rich clear brown, but appear almost black when viewed en masse. 
Inferiorly each spore has an elongated stem, by which it is permanently attached 
to the host-plant. They occur in elongated patches upon the straw, sometimes 
upon the glumes. Lach patch is surrounded by the torn everted edges of the epi- 
* For further ig of the germination of this and other Uredines, see Plowright, Greviliea, 
vol. t » p. 138, pl. x 
De Bary, Nea Untersuchungen iiber Uredineen, 186s, p. 24. 
