MELAMPSORIDIUM 359 
spores roundish, 14—21 x 11—16 y, echinulate; epispore thinner 
and smoother above. 
Uredospores. Sori hypophyllous, with yellow spots showing 
on the upper side, collected in groups and mostly limited by 
the veins, each sorus scarcely ;4, mm. wide, surrounded by a 
dome-shaped peridium which at length opens at the summit 
(where its cells are drawn out into long sharp points, Fischer) ; 
spores decidedly oblong or subclavate, orange, 22—40 x 8—12 uw; 
epispore colourless, with distant spines, often smooth above. 
Fig. 268. 2. betulinum. Sorus of teleutospores. The fusion-nucleus 
is seen in four of them. x 600. 
Teleutospores. Sori hypophyllous, always covered by the 
epidermis, scarcely 4 mm. wide, in dense clusters limited by 
the veins, often spread over the whole leaf, reddish, then brown ; 
spores prismatic, rounded at both ends, somewhat oblique, 
80—50 x 7—15 4; epispore thin, scarcely thickened above, 
nearly colourless, without perceptible germ-pore. 
AKcidia on leaves of Laria europaea, May ; uredo- and teleu- 
tospores on Betula alba (both verrucosa and pubescens), August 
—November, lasting through the winter on the decaying leaves. 
(Figs. 267, 268; see also Fig. 37, p. 78.) 
It was Plowright who first, in 1890 (after many unsuccessful trials) 
discovered that the Melampsora on Birch was connected with an zcidium- 
form on Larch (see Zeitschr. f. Pflanzenkr. i. 130; Gard. Chron. 1890, viii. 
41). He performed the experiment in both directions, and his conclusions 
were confirmed, eight years later, by Klebahn. The ecidium in this cage 
does not belong to the czoma-type, but to that of Peridermium (P. Laricis 
Kleb.), having a peridium and resembling in its spores also Peridermium 
Strobi. The forms on B. verrucosa and B. pubescens are, to a small extent, 
