. The British rust fungi (Uredinales) their biology and classification. Rust fungi. ON COMPOSITjE 153 purplish spots, scattered, minute, punctiform, soon naked, brown; spores few, globose to ovate, echinulate, brown, 22— 32 X 19—26/i, with two germ-pores. Teleutospores. Sori similar, but darker; spores ellipsoid to oblong, rounded at both ends, not thickened above, not con-. Pig. 105. P. variabilis, ^oidia, on leaf of Taraxacum, and teleutospore. stricted, delicately verrueulose, brown, 28—40 x 18—25 /j,; epispore thin; pedicels hyaline, about as long as the spore, but deciduous. On Taraxacum
. The British rust fungi (Uredinales) their biology and classification. Rust fungi. ON COMPOSITjE 153 purplish spots, scattered, minute, punctiform, soon naked, brown; spores few, globose to ovate, echinulate, brown, 22— 32 X 19—26/i, with two germ-pores. Teleutospores. Sori similar, but darker; spores ellipsoid to oblong, rounded at both ends, not thickened above, not con-. Pig. 105. P. variabilis, ^oidia, on leaf of Taraxacum, and teleutospore. stricted, delicately verrueulose, brown, 28—40 x 18—25 /j,; epispore thin; pedicels hyaline, about as long as the spore, but deciduous. On Taraxacum officinale and its variety palustre. July— October Not common. (Fig. 105.) Plowright and Sopjjitt both proved, Dy laying leaves affected with the seoidium of this species on healthy plants of Taraxacum, that the viredo- and teleutospores were produced in about fourteen days. In July the three spore-forms may be found on the same leaf. There are two forms of aecidium found upon Taraxacum; one, ^cidium Grevillei Grove { = JE. Taraxad Grev. non K. et S.), spreads pretty uniformly over the whole leaf in "numerous little clusters with single ones scattered between them," as Greville describes it (Flor. Bdin. p. 444)—the other, jS. Taraxad K. et S., forms large round clusters, and belongs to P. silvatica. Fischer points out that the two secidia differ in the form of their peridium cells, those of P. variabilis having the membrane thickened on the inner side, while those of P. silvatica have the outer wall most strongly thickened. He states, furthermore, that it will be found that this difference is characteristic in general of autcecious and heteroecious species respectively. It is not, however, universally so, the secidium of P. albescens has the outer wall much more strongly thickened, although it is autcecious. Greville figures the teleutospores of his species (Soot. Crypt. Flor. pi. 75) as having either one or both of the cells sometimes divided by a ve
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