THE RUST-FUNGI OF SUFFOLK.
THE
RUST-FUNGI
OF
B Y ARTHUR MAYFIELD,
55
SUFFOLK. F.L.S.
or Rusts are a group of parasitic fungi which attack the leaves, stems, and sometimes other parts of living phanerogams and ferns. A rust, during its various stages, raay produce as many as five different kinds of spore. In autcecious species the parasite completes its life-cycle on a single host • but in many species the earlier stages are produced upon one host, and the later ones, producing uredospores and teleutospores, are transferred to another host which can better accommodate the parasite during the autumn and winter—a phenomenon known as heteroecism. T H E UREDINALES
After the infection of a leaf by the entry of the Contents of a basidiospore, the presence of the rust makes itself evident by the appearance of yellow or brown pustules, generally on the upper surface of the leaf, followed by the formation of ajcidia or clustercups on the under surface. T h e former are pycnidia or spermogones producing pycnidiospores ; the latter, often beautiful objects, consist each of an outer wall or peridium enclosing vertical chains of yellow or golden ascidiospores. In a few cases the peridium is absent, and the ascidiospores form a pulverulent mass bursting through the epidermis of the host, and spreading over a considerable area. Such fructifications are called CEeomata and are conspicuous objects in early summer on brambles, roses, etc. Germ-tubes from the germinating secidiospores find' access through the: stomata, infecting fresh tissue, either on the same host, or, as in heteroecious rusts, on a host of an entirely different species. A new mycelium is formed in the intercellular spaces of the host and soon uredo-spores are produced. They occupy pulverulent yellow or brown sori, mostly on the under surface of the leaves. T h e uredospores, on germinating, reproduce their own kind again and again, and it is in this stage that the fungus spreads very rapidly. Later in the year teleutospores or winter spores" make their appearance, either among the uredospores or in separate sori. They are generally dark brown in colour, and are one-celled in the genus Uromyces, two-celled m Puccinia, three-celled in Triphragmium, or many-celled in Phragmidium and Xenodochus. Teleutospores are thick-walled and more durable, and their funetion is to preserve the chain of nfe during the winter. On germinating they produce basidiospores, generally four in number, from each cell. The lifehistory of a rust is not always so complex; in some species the ascidial stage is omitted and in others, such as the Hollyhock nist, only teleutospores and basidiospores are formed.