384 



BOTANY 



TAKT II 



from the multinucleate condition. Albugo tragopoijonis occupies an intermediate 

 position in that its oosphere is at first multinucleate, but later contains only one 

 female nucleus, the others having degenerated. The superfluous nuclei in the 

 oogonia and antheridia may be regarded as the nuclei of gametes which have 

 become functionless, and are comparable with the superfluous egg-nuclei of certain 

 Fucaceae. The oospores either produce a mycelium directly or give rise to 

 swarm -spores. 





Fi<:. 311.— Fertilisation of the Peronosporeae. 1, Perutiospora 

 jmrasitica. Young multinucleate oogonium (og) and anther- 

 idiuni (iiii). 2, Albugo candidn. Oogonium with the central 

 uninucleate oospliere and the fertilising tube (a) of the 

 antheriilium which introduces the male nucleus, o. Tliesame. 

 Fertilised egg-cell (o) surrounded by the periplasm (j)). (After 

 Waoer. X ti6ti.) 



Fig. 312. — Ilhizopus niiiricans { = Mwor sto- 

 lonifer). Portion of the mycelium with 

 three sporangia ; that to the right is shed- 

 ding its spores and shows the persistent 

 hemispherical columella, (x 38.) 



Order 2. Zygomycetes 



1. The Mucorineae ("-) comprise a number of the most common ]\Iould Fungi. 

 They are terrestrial and saprophytic, and are found chiefly on decaying vegetable 

 and animal substances. Asexual reproduction is efl"ected by non-motile, walled 

 spores, which either have the form of conidia or arise endogenously in sporangia. 

 Sexual reproduction consists in the formation of zygospores, as a result of the con- 

 jugation of two equivalent coenogametes. 



One of the most widely distriliuted species is 3fuc.or 3[ucrdo, fre(^ucntly found 

 forming white fur-like growths of mould on damj^ bread, preserved Iruits, dung, 

 etc. Mucor stolonifer { = Rhizoims nigricans), with a brown mycelium, occurs on 

 similar substrata. The spherical sporangia arc borne on the ends of thick, erect 

 branches of the mycelium (Fig. 312). From the apex of each sporangiophore a 

 single si)her)cal sporangium is cut olf by a transverse wall, which protrudes into 

 the cavity of the sporangium and forms a columella (Fig. 31.3, 1, c). The contents 

 of the sporangium become divided by re])cated cleavages into numerous spores. 



i 



