OOSPORES. 267 



minates only after a long period of rest, and does not then give rise at once to a 

 new mycelium of the ordinary kind; but the inner layer of the cell-wall bursts the 

 outer layer and protrudes through it in the form of a tube (Fig. 174 C), which 

 immediately developes into a conidiophore that breaks up into a number of conidia 

 each of which developes into a new mycelium. This behaviour is evidently analogous 

 to the germination of the zygospores of Pandorina, and to that of the oospores of 

 (Edogonium and Cystopus hereafter to be described, which do not however produce 

 conidiophores, but a number of zoospores which give birth to new individuals. 

 The zygospore may therefore be considered as a sporocarp, forming, together with 

 its conidiophores, a second generation, only that the carpospores are here precisely 

 like the ordinary non-sexual conidia. 



In our present state of knowledge the. Zygomycetes may be divided into two 

 famiUes : — 



1. The Mucorini, in which the conidia are formed, by free cell-formation, in 

 the interior of spherical receptacles. In the genus Mucor the conidia are set free by 

 the bursting of the fragile wall of the receptacle, while in Pilobolus this remains 



lintact, but when ripe becomes detached at its base and, together with the conidia, 

 [is thrown to a distance by its elasticity. Mucor Mucedo is one of the commonest 

 [moulds, being found on fruits, bread, dung, and even in the interior of nuts and 

 [apples into which the mycelium penetrates. Mucor stolonifer covers in a short space 

 of time large pieces of the same substrata, the mycelium putting out long stolon-like 

 (branches which attach tjiemselves by their extremity, and produce conidiophores with 

 [black heads. The mycelium can even penetrate through the shell of fresh-laid eggs, 

 and form conidiophores within them. Phycomyces nitens (Fig. 174 B) is distinguished by 

 its conidiophores, which are ten or fifteen centimetres in height and of a violet colour. 

 Ihamnidium bears an ordinary large conidiophore at the summit of each of the long 

 stalks, and below these whorls of small branches with very small receptacles containing 

 only a few conidia. Pilobolus almost always makes its appearance when fresh horse-dung 

 is covered by a bell-glass^. 



2. The Piptocephalidae bear a number of stylogonidia on their conidiophores which 

 are much branched towards the summit. The two genera described by Brefeld, 

 Chcetocladium and Piptocephalis, are parasitic upon Mucor Mucedo^ the latter being 

 represented in Fig. 175. 



I 



CLASS III. 



OOSPORES. 



To this class belong all those Thallophytes, whether containing chloro- 

 phyll or not, which are reproduced sexually by means of oogonia. An Oogo- 

 nium is a cell distinguished by its size and shape; the contents either form 

 a naked primordial cell — the Germ-cell or Oosphere — by simple contraction and 

 rounding off within the oogonium, which opens later, or divide into two 

 or more portions, which similarly become oospheres. The fertilisation of 

 these oospheres is effected by means of motile Antherozoids produced within 



^ [On Pilobolus crystalUnus see Cohn, Nova Acta Acad, Nat. Curios, vol. XV. pt. I. p. 370. — 

 KJeiii in Pringshciin s Jahrb. flir wiss. Bot. vol. VIII.] 



