A, affected growths of Hybrid Perpetual Roses: a, first or summer growth which has been shortened after flowering to induce vigorous second growths to push for the second blooming; b, second or so-called autumnal shoots; c, an attack of fungus on the wood; d, leaves infested.
B, the summer form of the fungus, popularly known as mildew: e, the surface of the leaf; f, the mycelium of the fungus; g, a conidiophore having conidia or spores, X 300.
C, the winter form of the fungus, a minute, blackish perithecium, immersed in felted mycelium on the leaves or shoots: A, perithecium; i, appendages, X 100.
D, the breaking up of the perithecium in the spring or early summer: j, the perithecium broken up in which the ascus has been kept during the winter; k, ascus free and discharging spores, X 200.
E, winter spore germinating: l, spore; m, germ tube, X 200.
F, summer spore germinating: n, spore; o, germ tube, X 300.