348 



BOTANY 



which protrudes into the cavity of the sporangium and forms a columella (Fig. 

 270, 1, c). The contents of the sporangium separate into numerous oval spores 

 embedded in a mass of gelatinous matter capable of great expansion. The wall of 

 the sporangium is easily ruptured, and the spores are discharged by the swelling 

 of the interstitial mass, leaving the columella entirely exposed (Fig. 270, 1, 5, 2). 



Under certain conditions, instead of asexual sporangia, organs of sexual repro- 

 duction are produced. The hyphae of the mycelium then give rise to lateral, club- 

 shaped gametophores. "When the tips of two gametophores come into contact, a 

 conjugating cell or gamete is cut off from each by a transverse wall (Fig. 271, 1, 2, 3). 

 The two cells thereupon coalesce, and fuse into a zygospore, the outer wall of 

 which is covered with warty protuberances (4). After a period of rest the zygospore 



Fig. 270. — 1-4, Mucor Mucedo. 1, A sporangium in optical longitudinal section ; c, columella ; m, 

 wall of sporangium ; sp, spores ; 2, a ruptured sporangium with only the columella (c) and a small 

 portion of the wall (m) remaining ; 3, two smaller sporangia, with only a few spores and no 

 columella ; 4, germinating spore ; 5, ruptured sporangium of Mucor mucilagineits with deli- 

 quescing wall (m)and swollen interstitial substance (js) ; sp, spores. (After Brefeld, 1x225, 

 2-5 X 800.) 



develops a germ-tube, which may at once bear a sporangium (5). The conjugating 

 hyphae take their rise in exactly the same way as sporangiophores, of which they 

 may accordingly be regarded as sexually differentiated rudiments. 



Within the group of the Zygomycetes also, a reduction of sexuality is perceptible. 

 Thus, in the case of certain Mucorineae, although the conjugating hyphEe meet in 

 pairs, no fusion takes place, and their terminal cells become converted directly 

 into spores, which are termed AZYGOSpoees. In other forms again, hyphae 

 producing azygospores are developed, but remain solitary, and do not, as in the 

 preceding case, come into contact with similar hyphse. 



Both the size and number of spores produced in the sporangia of Mucor 

 Mucedo are subject to variation (of. Fig. 270, 1, 3). The sporangia of the genera 

 Thamnidium are, on the other hand, regularly dimorphous, and a large sporangium 

 containing many spores is formed at the end of the main axis of the sporangiophore, 

 while numerous small sporangia, having but few spores, are produced by its 

 verticillately branching lateral axes. The sporangia may at times develop only 



