674 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



but a single spore. Whilst the bulk of Mucoraceae are saprophytes on animal ex- 

 creta, &c., a certain number are parasitic on Mucor itself as well as other Fungi. 



The MortierellecB, though in general resembling Mucoraceae, are distinguished by 

 the fact that their zygospores become invested in a plexus of mycelial hyphse which 

 form a sort of pericarp around the fruit. The base of the sporangial hypha also is 

 invested in a sort of bird's-nest. This condition is of interest as it leads on to the 

 more complex fruits of higher Fungi. 



The Zygomycetes include 125 species. 



Sub-Class II. — Mesomtcetes. 



Mycelium multicellular; asexual reproduction alone is known by means of 

 spores (not limited in number) developed in sporangia; or by conidia. They are 

 regarded as occupying an intermediate position between the lower Fungi and the 

 two large groups of higher Fungi, the Ascomycetes and Basidiomycetes respectively. 



Alliance XVI. — Hemiasci. 



Tube-like sporangia containing an unlimited number of spores. This alliance 

 leads on to the Ascomycetes. 



Families : Ascoidece, Protomycetes, Theleholeoe. 



These are mostly simple forms of parasites characterized by the indefinite 

 number of spores contained in their sporangia. Some of them produce chlamydo- 

 spores freely. Thelebolus is interesting in that its sporangium is inclosed in a 

 cortex and may be compared with Mortierella of the Zygomycetes on the one hand, 

 and with the corticated Ascomycetes (carpo-asci) on the other. 



There are about 20 species belonging to this alliance. 



Alliance XVII. — Hemibasidii. 



Parasites with a septate mycelium, which forms numerous chlamydospores. 

 From these spores a promycelium is developed on which conidia (sporidia) are 

 produced. No sporangia are formed. This alliance is thought to lead on to the 

 Basidiomycetes. 



Families: UstilaginaceoB, Tilletiacece. 



These are all parasitic forms, and are known as the Smuts. The mycelium grows 

 in the living tissues of the host, and concludes its development with the production 

 of chains of chlamydospores (cf. p. 673), which are provided with a thick 

 membrane, and are usually dark in colour. It is in respect of this character that the 

 name " Smut " has been given. Very often these chlamydospores are produced in 

 connection with the fruiting organs of the host-plant (various Grasses, &c.). The 



