lOO British UredinecE and UstilaginecB. 



plant, but this is probably incorrect. To Wolff,* however, 

 we owe the first accurate explanation of this process. He 

 investigated it with U. segetiiui and niaydis, Urocystis occulta 

 and T. tritici. 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 T. tritici 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 Urocystis 

 occulta the investing sheath exists only where the mycelium 

 passes through the first epidermal cell. Kuhn j 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 tlie 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 T. Critic/ and planting it, it became 

 affected with bunt, yet with 0". segctuiii such dusting rarely, 

 if ever, succeeds in producing the disease, Hoffmann was 

 able to produce only a few smutted plants in many hundred 



* Wolf, " Roggenstengelbiand," Bot. Zcituug {\%-Ji), t. viii. ; " Der 

 Brand des Getreides" (1874), pp. 18-24, t. iii., iv. 



t \\x\\w\, Bot. Z£7V//;/^(i874), pp. 121-124; Fahlingsladw. Zcitimj [i^-]g) 

 p. 84. 



