_Peronospora_, to which De Bary considers _Cystopus_ to be closely allied. At all events, this is a peculiarity of structure and development not as yet met with in any other of the _Cæomacei_. In _Uromyces_ is the nearest approach to the _Pucciniæi_; in fact, it is _Puccinia_ reduced to a single cell. The form of spore is usually more angular and irregular than in _Trichobasis_, and the pedicel is permanent. It may be remarked here, that of the foregoing genera, many of the species are not autonomous that have hitherto been included amongst them. This is especially true of _Lecythea_, _Trichobasis_, and, as it now appears, of _Uromyces_.[e] [Illustration: FIG. 19.--_Cystopus candidus._] [Illustration: FIG. 20.--_Xenodochus carbonarius._] [Illustration: FIG. 21.--_Phragmidium bulbosum._] PUCCINIÆI.--This group differs from the foregoing chiefly in having septate spores. The pustules, or sori, break through the cuticle in a similar manner, and here also no true peridium is present. In _Xenodochus_, the highest development of joints is reached, each spore being composed of an indefinite number, from ten to twenty cells. With it is associated an unicellular yellow Uredine, of which it is a condition. Probably, in every species of the _Pucciniæi_, it may hereafter be proved, as it is now suspected, that an unicellular Uredine precedes or is associated with it, forming a condition, or secondary form of fruit of that species. Many instances of that kind have already been traced by De Bary,[f] Tulasne, and others, and some have been a little too rashly surmised by their followers. In _Phragmidium_, the pedicel is much more elongated than in _Xenodochus_, and the spore is shorter, with fewer and a more definite number of cells for each species; Mr. Currey is of opinion that each cell of the spore in _Phragmidium_ has an inner globose cell, which he caused to escape by rupture of the outer cell wall as a sphæroid nucleus,[g] leading to the inference that each cell has its own individual power of germination and reproduction. In _Triphragmium_, there are three cells for each spore, two being placed side by side, and one superimposed. In one species, however, _Triphragmium deglubens_ (North American), the cells are arranged as in _Phragmidium_, so that this represents really a tricellular _Phragmidium_, linking the present with the latter genus. In _Puccinia_ the number of species is by far the most numerous; in this genus the spores are uniseptate, and, as in all the _Pucciniæi_, the peduncles are permanent. There is great variability in the compactness of the spores in the sori, or pulvinules. In some species, the sori are so pulverulent that the spores are as readily dispersed as in the Uredines, in others they are so compact as to be separated from each other with great difficulty. As might be anticipated, this has considerable effect on the contour of the spores, which in pulverulent species are shorter, broader, and more ovate than