G. globosum is another species forming cedar apples, but the gelatinous strings of teleutospores are short and clavate, and the cluster-cups are formed on hawthorns. G. nidusavis forms “witches brooms” or “birds nests” in the branches of the cedar. The mycelium in the branches stimulates them to profuse branching so that numerous small branches are developed close together. The teleutosori form small pustules scattered over the branches. G. clavipes affects the branches of cedar only slightly deforming them or not at all, and the cluster-cups are formed on fruits, twigs, and leaves of the hawthorns or quinces, the cluster-cups being long, tubular, and orange in color. CHAPTER XXI. THE HIGHER FUNGI. =411. The series of the higher fungi.=—Of these there are two large series. One of these is represented by the sac fungi, and the other by the mushrooms, a good example of which is the common mushroom (Agaricus campestris). Sac Fungi (Ascomycetes). =412. The sac fungi= may be represented by the “powdery mildews”; examples, uncinula, microsphæra, podosphæra, etc. Fig. 225 is from a photograph of two willow leaves affected by one of these mildews. The leaves are first partly covered with a whitish growth of mycelium, and numerous chains of colorless gonidia are borne on short erect threads. The masses of gonidia give the leaf a powdery appearance. The mycelium lives on the outer surface of the leaf, but sends short haustoria into the epidermal cells. =413. Fruit bodies of the willow mildew.=—On this same mycelium there appear later numerous black specks scattered over the affected places of the leaf. These are the fruit bodies (_perithecia_). If we scrape some of these from the leaf, and mount them in water for microscopic examination, we shall be able to see their structure. Examining these first with a low power of the microscope, each one is seen to be a rounded body, from which radiate numerous filaments, the _appendages_. Each one of these appendages is coiled at the end into the form of a little hook. Because of these hooked appendages this genus is called _uncinula_. This rounded body is the _perithecium_. [Illustration: Fig. 225. Leaves of willow showing willow mildew. The black dots are the fruit bodies (perithecia) seated on the white mycelium.] =414. Asci and ascospores.=—While we are looking at a few of these through the microscope with the low power, we should press on the cover glass with a needle until we see a few of the perithecia rupture. If this is done carefully we see several small ovate sacs issue, each containing a number of spores, as shown in fig. 227. Such a sac is an _ascus_, and the spores are _ascospores_. [Illustration: Fig. 226. Willow mildew; bit of mycelium with erect conidiophores, bearing chain of gonidia; gonidium at left germinating.] [Illustration: Fig. 227. Fruit of willow mildew, showing hooked appendages. Genus uncinula.]