Scanning electron micrograph (SEM) of a pathogenic fungus, Erisyphe pisi, also known as E. polygoni, which causes powdery mildew in cereals, clover, & peas. Economically disastrous, the infection begins with capsule-like spores (conidia) like the one at upper centre. These produce a short germ tube, which attaches to the leaf surface (in this case of a pea) with a pad or appressorium. A tube grows from under the pad into the leaf epidermis. If the plant is susceptible, the tube produces outgrowths inside the leaf; a thread-like mycelium covers the leaf surface & produces conidiophores (bulbous tips) which bear new conidia. Magnificat- ion: x40 at 35mm size, x300 at 8x10-inch size. Reference: MICROCOSMOS, figure 5.31, page 104.