3IO PART IV. VEGETABLE TAXONOMY. 



mycelial filaments. These most frequently occur on the inflor- 

 escence, or on parts adjacent to it, and the spore-masses, together 

 with the abnormal growth caused by it, often assume quite char- 

 acteristic forms. Corn-smut forms irregular, roundish-lobed 

 masses, often attaining a diameter of six inches or more. The 

 masses consist of a translucent gelatinous membrane enclosing 

 innumerable blackish-brown, rounded spores, having a nodular 

 surface. The spores, in many species at least, do not, when 

 germinating, at once produce the slender mycelial threads 

 already described, but give rise to a pro-mycelium from which 

 cells are separated, which develop into a true mycelium. In 

 some instances, however, these secondary spores have been 

 observed to conjugate. 



The Phycomycetes. 



The term Phycomycetes literally means " Sea-weed Fungi," 

 and alludes to the resemblance, in the mode of sexual reproduc- 

 tion, between these plants and certain of the Algae. They pro- 

 duce a copious mycelium, which usually consists of unsegmented 

 hyphae, bear conidia, and most of them reproduce sexually either 

 by zygospores or oospores. 



There are three sub-orders, the Zygomycetes, the Peronosporece, 

 and the Saprolegniecz. 



Of the Zygomycetes, or Conjugating-Fungi, Mucor Mucedo 

 may be taken as an example. This mould is a very common 

 one found growing on various kinds of decaying matters, such 

 as horse-dung, rotten fruits, etc. The hyphae branch profusely 

 through the substratum, whatever it may be, deriving nourish- 

 ment from it. The fruiting hyphae, however, are simple, and 

 grow out into the air, each bearing at its tip a globular, blackish 

 sporangium, the wall of which soon ruptures, setting free numer- 

 ous conidia. This is the asexual mode of reproduction. Sexual 

 reproduction takes place by the conjugation of some of the 

 interior hyphae. The large, rounded, nodular zygospores are 

 formed between the filaments. These rest fur a time before 

 germinating, and then, if the supply of nourishment is sufficient, 

 develop a copious vegetative mycelium ; if insufficiently nour- 

 ished they produce at once aerial hyphae, bearing sporangia. 

 The modes of reproduction in this plant are illustrated in Fig. 509. 



