The germination in Æcidium has been followed out by Tulasne,[F] either by placing the pseudospores in a drop of water, or confining them in a moist atmosphere, or by placing the leaves on which the Æcidium flourishes upon water. The pseudospores plunged in water germinated more readily than the others. If the conditions were favourable, germination would take place in a few hours. Æcidium Ranunculacearum, D. C., on leaves of figwort, gives rarely more than one germinating filament, which soon attains three times the length of the diameter of the pseudospore. This filament generally remains simple, sometimes torulose, and distorted in a long spire. Sometimes it has been seen divided into two branches, nearly equal to each other. The spore in germinating empties itself of its plastic contents, contracts, and diminishes in size. The pseudospores of Æcidium crassum, P., emit three long filaments, which describe spirals, imitating the twistings of the stem of a bean or bindweed. In Æcidium Violæ, Schum, one filament is produced, which frequently rolls up its anterior extremity into a spire, but more often this same extremity rises in a large ovoid, irregular vesicle, which continues the axis of the filament, or makes with it a more or less decided angle. In whatever manner placed, this vesicle attracts to it all the orange protoplasm, and hardly does this become settled and complete before the vesicle becomes the starting point of a new development, for it begins to produce at its apex a filament, more slender than the previous one, stiff, and unbranched.
Fig. 81.—Germination of Æcidium Euphorbia (sylvaticæ), Tulasne.
According to M. Tulasne, the germination of the pseudospores of Æcidium Euphorbiæ on Euphorbia sylvatica differ in some respects from the preceding. When dropped upon water these spores very soon emit a short tube, which ordinarily curves in an arch or circle, almost from its origin, attaining a length of from three to six times the diameter of the spore; then this tube gives rise to four spicules, each of which produces a small obovate or reniform sporule; the generation of these sporules absorbs all the plastic matter contained in the germ-tube, which permits of the observation that it was divided into four cells corresponding with the number of spicules. These sporules germinate very rapidly from an indefinite point of their surface, emitting a filiform process, which is flexuous and very delicate, not extending more in length than three times that of the long axis of the sporule, often less, reproducing at its summit a new sporule, differing in form and size from that which preceded it. This sporule of the second formation becomes at its apex a vital centre, and sprouts one or more linear buds, of which the elongation is occasionally interrupted by the formation of vesicular swellings. As Tulasne observes, the pseudospores of the Æcidium and the greater number of Uredines are easily wetted with water before arriving at maturity; but when they are ripe, on the contrary, they appear to be clothed with a greasy matter which protects them from the liquid, forcing them almost all to rest on the surface.
The pseudospores of Rœstelia are produced in strings or chaplets, as in Æcidium, with this difference, that instead of being contiguous they are separated by narrow isthmuses. The ripe pseudospores are enveloped in a thick tegument, of a dark brown colour. They germinate readily on water, producing a filament fifteen times as long as the diameter of the spore. This filament is sometimes rolled or curved. Towards its extremity it exhibits protuberances which resemble the rudiments of ramuli, or they terminate in a vesicle which gives rise to a slender filament. The tegument of these pseudospores, above all in those which have germinated, and have consequently become more transparent, it is easy to see has many pores, or round ostioles.
In Peridermium the pseudospores, when dropped upon water, germinate at any point of their surface. Sometimes two unequal filaments issue from the same spore. After forty-eight hours of vegetation in the air, the greater part had already emitted a multitude of thick little branches, themselves either simple or branched, giving to the filaments a peculiar aspect. Tulasne did not on any occasion observe the formation of secondary spores.
Fig. 82.—Germinating pseudospores of (b) Coleosporium Sonchi; (s s) secondary spores, or sporules (Tulasne).
In the Uredines proper the germination seems to be somewhat similar, or at least not offering sufficient differences to warrant special reference in Uredo, Trichobasis, Lecythea, &c. In Coleosporium there are two kinds of spores, one kind consisting of pulverulent single cells, and the other of elongated septate cells, which break up into obovate joints. Soon after the maturity of the pulverulent spores, each begins to emit a long tube, which is habitually simple, and produces at its summit a reproductive cellule, or reniform sporule. The orange protoplasm passes along the colourless tubes to the terminal sporule at the end of its vegetation. The two forms of spores in this genus are constantly found on the same leaf, and in the same pulvinule, but generally the pulverulent spores abound at the commencement of the summer. The reniform sporules begin to germinate in a great number as soon as they are free; some few extend a filament which remains simple and uniform, but more commonly it forms at its extremity a second sporule. If this does not become isolated, to play an independent life, the filament is continued, and new vesicles are repeated many times.
