ZYGOMYCETES. 1 1 5 



but by conjugation or union of two cells of the mycelium 

 separated off from the ends of two hyphae by transverse walls. 

 As a result of conjugation, a zygospore is produced, which is 

 a resting-spore and corresponds to the oospore of the Oomycetes. 

 The zygospore puts forth a germ-tube, which becomes a mycelium 

 bearing sporangia on sporangiophores. From each sporangium, 

 spores, never swarm-spores, are set free, germinate, and produce 

 a mycelium. Sporangia similar in form to the zygospores may 

 be asexually produced on the mycelium. The unicellular and 

 much-branched mycelium grows into its substratum, and is 

 nourished as a rule saprophytically. The Entomophthoreae cause 

 important insect-diseases on Muscidae, Cabbage Butterflies, and 

 caterpillars of Trachea piniperda (the Pine Beauty). 



Another common group of the Zygomycetes, the Mucorini, 

 penetrate into bruised places in living fruits, and produce decay 

 (see p. 180). Some other Zygomycetes are parasitic on fungi 

 ^Conidioiolits), some on animals. 



(3) OOMYCETES. 



These fungi possess a one-celled and much-branched mycelium. 

 In their vegetative structure they most nearly resemble algae 

 like Vaucheria. Eeproduction is brought about, asexually by 

 means of swarm-spores formed in sporangia (conidia also occur) ; 

 sexually by oospores derived from oogonia and antheridia. 



There are three families of Oomycetes : Saprolegniaceae, Mono- 

 Uepharideae and Peronosporeae. Two of these groups contain 

 parasitic forms : Saprolegniaceae (e.g. Achyla prolifera, dangerous 

 to Fish and Crustaceans) ; and Peronosporeae. 



PERONOSPOREAE. 



The greater number of the Peronosporeae live as parasites in 

 the tissues of higher plants, and obtain nourishment generally by 

 means of haustoria. The mycelium, iu earlier life at least, has no 

 dividing septa, and generally grows in the intercellular spaces of 

 the host-plant, and sends haustoria into the cells. Eeproduction 

 is effected asexually by formation of swarm-spores in sporangia, 

 and sexually by means of oospores. The latter are produced 

 from the fertilization of an ovum in an oogonium by an antheridium 

 whose contents pass through a fertilization-tube penetrating the 



