=433. Order Chytridiales (Chytridineæ).=—These include the lowest fungi. Many of them are parasitic on algæ and lack mycelium, the swarm spore either with or without minute rhizoids, developing into a globose sporangium (Rhizophidium, Chytridium, Olpidium, etc., fig. 249), or the swarm spore attached to the wall of the host develops into a long sword-shaped body with a sterile base, which proliferates and forms a new sporangium in the old one (Harpochytrium), or with slight development of mycelium in aquatic plants (Cladochytrium). Some are parasitic in leaves and stems of land plants. Synchytrium decipiens is very common on the trailing legume, Amphicarpæa monoica. =434. Order Ancylistales (Ancylistineæ).=—The members of this order have a slight development of mycelium and many are parasitic in algæ (Lagenidium, fig. 249). =435. Order Saprolegniales (Saprolegniineæ).=—These include the water molds (Saprolegnia). See Chapter XIX. =436. Order Monoblepharidales (Monoblepharidineæ).=—These are peculiar water molds, related to the Saprolegniales, but motile sperm cells are formed (Monoblepharis, etc., fig. 250). =437. Order Peronosporales (Peronosporineæ).=—These include the downy mildews (Peronospora, Plasmopara, Phytopthora, etc.), and the white rust of crucifers and other plants (Cystopus = Albugo), Chapter XIX. 2. SUBCLASS ZYGOMYCETES. =438.= These are the conjugating fungi. =439. Order Mucorales (Mucorineæ).=—This includes the black mold and its many relatives (Mucor, Rhizopus, etc.). Chapter XIX. =440. Order Entomophthorales (Entomophthorineæ).=—This order includes the “fly fungus” (Empusa) and its many relatives parasitic on insects. In the autumn and winter dead flies are often found stuck to window-panes, with a white ring of the conidia around each fly. II. Class Ascomycetes. (The ascus series.) 1. SUBCLASS HEMIASCOMYCETES. [Illustration: Fig. 251. Dipodascus albidus. _A_, thread with sexual organs, ascogonium and antheridium; _B_, fertilized ascogonium developing ascus; _C_, ascus with spores; _D_, conidia. (After Lagerheim.)] =441. Order Hemiascales (Hemiascineæ).=—Fungi with a well developed, septate mycelium, but with a sporangium-like ascus, i.e., a large and indefinite number of spores in the ascus. Examples: Protomyces macrosporus in stems of Umbelliferæ, or P. polysporus in Ambrosia trifida. These two are by some placed in the Ustilagineæ. Dipodascus albidus grows in the exuding sap of Bromeliaceæ in Brazil and the sap of the beech in Sweden. The ascus is developed as the result of the fertilization of an ascogonium with an antheridium (see fig. 251). 2. SUBCLASS PROTOASCOMYCETES. =442. The asci are well-defined= and usually with a limited and definite number of spores (usually 8, sometimes 1, 2, 4, 16, or more). Mycelium often well developed and septate. Asci scattered on the mycelium, not associated in definite fields or groups.