in the compact species. If a section of one of the more compact sori be made, it will be seen that the majority of the spores are side by side, nearly at the same level, their apices forming the external surface of the sori, but it will not be unusual to observe smaller and younger spores pushing up from the hymenial cells, between the peduncles of the elder spores, leading to the inference that there is a succession of spores produced in the same pulvinule. In _Podisoma_, a rather anomalous genus, the septate spores are immersed in a gelatinous stratum, and some authors have imagined that they have an affinity with the Tremellini, but this affinity is more apparent than real. The phenomena of germination, and their relations to _Roestelia_, if substantiated, establish their claim to a position amongst the _Pucciniæi_.[h] It seems to us that _Gymnosporangium_ does not differ generically from _Podisoma_. In a recently-characterized species, _Podisoma Ellisii_, the spores are bi-triseptate. This is, moreover, peculiar from the great deficiency in the gelatinous element. In another North American species, called _Gymnosporangium biseptatum_, Ellis, which is distinctly gelatinous, there are similar biseptate spores, but they are considerably broader and more obtuse. In other described species they are uniseptate. [Illustration: FIG. 22.--Pseudospores of _Puccinia_.] USTILAGINEI.--These fungi are now usually treated as distinct from the _Cæomacei_, to which they are closely related.[i] They are also parasitic on growing plants, but the spores are usually black or sooty, and never yellow or orange; on an average much smaller than in the _Cæomacei_. In _Tilletia_, the spores are spherical and reticulated, mixed with delicate threads, from whence they spring. In the best known species, _Tilletia caries_, they constitute the "bunt" of wheat. The peculiarities of germination will be alluded to hereafter. In _Ustilago_, the minute sooty spores are developed either on delicate threads or in compacted cells, arising first from a sort of semi-gelatinous, grumous stroma. It is very difficult to detect any threads associated with the spores. The species attack the flowers and anthers of composite and polygonaceous plants, the leaves, culms, and germen of grasses, &c., and are popularly known as "smuts." In _Urocystis_ and _Thecaphora_, the spores are united together into sub-globose bodies, forming a kind of compound spore. In some species of _Urocystis_, the union which subsists between them is comparatively slight. In _Thecaphora_, on the contrary, the complex spore, or agglomeration of spores, is compact, being at first apparently enclosed in a delicate cyst. In _Tuburcinia_, the minute cells are compacted into a hollow sphere, having lacunæ communicating with the interior, and often exhibiting the remains of a pedicel. [Illustration: FIG. 23.--_Thecaphora hyalina._] [Illustration: FIG. 24.--_Æcidium Berberidis._]