100 British Uvedinee and Ustilaginee. 
plant, but this is probably incorrect. To Wolff,* however, 
we owe the first accurate explanation of this process. He 
investigated it with U. segetum and maydis, Urocystis occulta 
and 7. tritic?. The outcome of his observations is that 
the germ-tube of the promycelial spores of the species is 
capable of piercing the embryonic plant at any time before 
the primary enveloping sheath of the young plant is 
ruptured. The germ-tubes of 7. ¢vztzc2 squeeze their points 
through the epidermal cells of the young plant, at first 
piercing through the outer epidermis of the primary sheath ; 
they then grow through the cells of the sheath itself, then 
through the inner epidermal cells of the sheath, across the 
interspace to the outer epidermal cells of the embryo, and 
so into the embryo itself (Plate VI. Fig. 2). With certain 
species the entering germ-tube acquires for itself an invest- 
ing sheath from the cells through which it passes (Plate VI. 
Fig. 3)—a sort of invagination of the outer wall of the outer 
epidermal cell, which is continued over the young mycelium 
as it grows through one cell after another. With Uvocystds 
occulta the investing sheath exists only where the mycelium 
passes through the first epidermal cell. Kiihnf subse- 
quently repeated and confirmed Wolff's observations as far 
as they went, but he also found that the germ-tubes could 
enter, not only through the primary sheath-leaf, but also 
into the true root-node at the base of the sheath, and, in 
point of fact, into almost any part of the embryo. While it 
has long been known that, by merely dusting wheat with 
the teleutospores of 7. ¢r¢tzcz and planting it, it became 
affected with bunt, yet with U. segetum such dusting rarely, 
if ever, succeeds in producing the disease. Hoffmann was 
able to produce only a few smutted plants in many hundred 
* Wolf, ‘‘ Roggenstengelbrand,” ot. Zeitung (1873), t. viii; “ Der 
Brand des Getreides” (1874), pp. 18-24, t. iii., iv. 
+ Kiihn, Bot, Zeitung (1874), pp. 121-124; Fahlingsladw, Zeitunz (1879) 
p. 84. 
