As an example of one of the most highly developed species, _Puccinia graminis_, the “Rust of Wheat,” holds a prominent position. Its uredospores and teleutospores are produced (Fig. 146) on Grasses (on cereals, especially Wheat, Rye, Oats, and many wild Grasses), while the æcidia and spermogonia are confined to the Berberidaceæ. The teleutospores, developed on the Grasses, hibernate on the dried portions of their host, and in the succeeding year each of the two cells of the teleutospore may develop a _basidium_ with four basidiospores (Fig. 146 _D_, _c_). The basidiospores are distributed by the wind, germinate quickly, and only proceed to further development on _Berberis_ or _Mahonia_. The germ-tube _bores through the epidermis_ of the Barberry-leaf, and forms a mycelium in its interior, its presence being indicated by reddish-yellow spots on the leaf. After 6–10 days the flask-shaped _spermogonia_ appear (Fig. 147 _B_; _C_, _a_; conidia in Fig. 147 _D_) and a few days later the cup-shaped _æcidia_ (Fig. 147 _A_; _C_, _c_, _d_, _e_). The former are generally on the _upper_, and the latter on the _under side_ of the leaf. The orange-coloured æcidiospores scatter like dust, and germinate only on Grasses; the germination takes place in about two days when placed on any green part of a Grass. The germ-tube enters the Grass-leaf through a stoma; a mycelium is developed in the leaf, giving rise to a small, oval, rust-coloured spot (Fig. 146 _A_); in about 6–9 days the epidermis is ruptured over the red spot, and numerous reddish-yellow _uredospores_, formed on the mycelium, are set free. The uredospores (Fig. 146 _B_) are scattered by the wind, and can germinate should they fall on the green portions of other Grasses: they then emit 2–4 germ-tubes through the equatorially-placed germ-pores. The germ-tubes enter a leaf through a stoma, a new mycelium is then developed, and in about eight days a fresh production of uredospores takes place, which germinate as before. The uredospore-mycelium very soon produces, in addition, the brown _teleutospores_, which give a brown colour to the rust-coloured spots, the familiar uredospores on the cereals being quite suppressed towards the close of the summer (Fig. 146 _C, D_). The “Rust of Wheat” hibernates on some wild Grasses in the uredospore-form. [Illustration: FIG. 147.--_Æcidium berberidis_. _A_ Portion of lower surface of leaf of Barberry, with cluster-cups (æcidia). _B_ A small portion of leaf, with spermogonia, from above. _C_ Transverse section of leaf on the upper side, in the palisade parenchyma are three spermogonia (_a b_); on the lower side an unripe æcidium (_c d_) and two ripe æcidia (_d, e, f_); _f_ chain of æcidiospores. _D_ Hyphæ, forming conidia.]