As an illustration of the life-history of a typical rust, the cycle of the heteroecious species Puccinia Caricis Schroet. is given below* This species is taken as a type because all spore stages are readily obtainable in New Zealand. This species was first suggested by W. B. Grove (1913) as a type in preference to P. graminis, as the aecidia are more easily obtained.:— In the early spring the teleutospore germinates and produces basidia, one from each cell; these grow out through the germ-pores, and, as they develop, the contents of the cells pass into them. Each basidium becomes four-celled when mature, and from each segment a sterigma is produced, from the apex of which a basidiospore is cut off by abstriction. The basidiospores are readily detached, and are carried by wind or other agency to leaves and shoots of plants growing in the vicinity. Should a basidiospore chance to alight on a young leaf or shoot of Urtica it germinates and produces a short hypha, which penetrates the cuticle and enters the host-tissues, where it rapidly branches and forms a subcuticular mycelium, which soon gives rise to small flask-shaped bodies, the spermogones.† Spermogones: Also known as “spermagonia,” “pycnidia,” or “pycnia.” The body of the spermogone is embedded in the host-tissues, the neck alone protruding; this is formed of numerous hair-like paraphyses (fig. 3) arranged in such a manner that a small circular or elliptical opening (ostiolum) is formed, through which the spermatia pass. The body is lined with hyphal Fig. 3.—Spermogone of Aecidium Ranuncularum: p, paraphysis; s, spermatium. × 500. Fig. 4.—Aecidium of Puccinia tasmanica Diet. from Senecio lautus Forst. f.: a, peridial cell; b, peridium; c, aecidiospore; d, host-tissues. × 250. filaments, from the apices of which colourless elliptical spermatia are abstricted. The spermatia are embedded in a mucilaginous substance which is said to be somewhat sweet to the taste, and in certain species possesses a strong aromatic smell; doubtless these two features serve to attract insects, and so ensure dispersion of the spermatia. The mucilage is strongly hygroscopic, and in the presence of moisture swells and is forced through the ostiolum, carrying the spermatia with it on to the surface of the host, where it readily dissolves away and leaves the spermatia behind (see fig. 3, s). As spermogones and spermatia are analogous to similar bodies found in the thallus of Collema, a genus of lichen, they were supposed to be male sexual organs, but as no corresponding female organ (trichogyne) has been