tubes are straight or twisted, simple or forked, and each of them becomes divided by transverse septa into four unequal cells towards their apex, from each of which is produced a spicule bearing a sporidium, or spherical secondary fruit, in the same manner as in the genera _Puccinia_ and _Aregma_. It should be observed, that the winter spores of this rust are borne on the opposite surface of the leaves to the summer spores: for whilst the latter are developed from the under surface, the former are found on the upper. This being also an instance of di-morphism, the summer condition, when spherical spores are produced, should not be regarded as a distinct plant, and the name of _Lecythea caprearum_ does not merit retention in the list of fungi. There are five species of this interesting group, or genus, found in Great Britain, to the residue of which we may only briefly allude. It has already been stated that, in summer, the yellow spores of a rust are found on the under surface of birch-leaves. These must be sought on the young twigs or suckers, proceeding from the stumps of trees which have been cut down: pale discoloured spots on the upper surface of the leaves indicate the presence of the rust beneath. This is the _Uredo betulina_ of old authors (begging their pardons, for some of them still live), the _Lecythea longicapsula_ of more recent times, and the summer spores of _Melampsora betulina_, according to M. Tulasne and his disciples. When fresh, it is reputed to exhale a faint odour, as of the primrose. During the winter and spring months the wedge-like spores of the second crop are matured on the fallen leaves (Plate IX. figs. 189, 190), and these are capable of a speedy germination, and the production of secondary reproductive bodies, as in the willow rust above alluded to. Probably, also, the similar rust on the poplar (Plate IX. figs. 195, 196), or on the aspen, may be met with under like conditions; _i.e._, the summer spores, which are yellow and spherical, on the living leaves, and the brown permanent masses of winter spores on the fallen and decaying leaves. The sole remaining British species is not uncommon on leaves of the common spurge in gardens, and whilst the yellow pulverulent spores occur on the upper, it will not be improbable that black permanent spots will be found on the lower leaves (Plate IX. figs. 193, 194), enclosing closely-packed, rudimentary, elongated or wedge-shaped cellules of the winter spores.