634 LECTURE XXII. 



Beginning with the Mucorini, we find that, in Mucor 

 Mucedo and Phycomyces nitens for instance, the zygospore 

 gives rise on germination to a rudimentary individual (promy- 

 celium} which is entirely asexual; from one of the spores 

 of this form a normal plant is developed, which produces 

 spores asexually but may also bear sexual reproductive 

 organs. Essentially the same life-history may be traced in 

 certain Peronosporeae (Phytophthora omnivora, Pythium proli- 

 ferum}\ in these the individual developed from the sexually 

 produced spore is always asexual, whereas that developed 

 from the asexually produced spore may be sexual, but it 

 always produces spores asexually. In these cases there is not 

 a strict alternation of generations, in consequence of the 

 succession of potential oophores, as in Coleochaete. 



In other cases the alternation is completely regular. In 

 the Ustilagineae, to begin with, the asexually produced spore 

 gives rise to a rudimentary individual (promycelium) which is 

 the sexual generation ; this produces sporidia which conjugate 

 in pairs, and from the product of conjugation springs the 

 individual which produces spores asexually. Essentially the 

 same life-history has been traced in some Ascomycetes and 

 Uredineae. In Claviceps, the sexually produced spore (as- 

 cospore) gives rise to an asexual form, long regarded as a 

 distinct genus under the name of Sphacelia, from the spores 

 of which the Claviceps is reproduced. In Sclerotinia (Peziza) 

 Fuckeliana, a similar regular alternation occasionally takes 

 place : the ascospore may give rise to an asexual form, long 

 known as Botrytis cinerea, from the spores of which the 

 Sclerotinia is in turn developed: but not infrequently the 

 ascospore gives rise to a Sclerotinia at once, in which case 

 there is of course no alternation. In Polystigma the ascospore 

 gives rise to a promycelium which bears sporidia, and these 

 sporidia give rise to the Polystigma. In Endophyllum 

 (Uredineae) the life-history is precisely the same as in Poly- 

 stigma; the promycelium is the sporophore, the sporidia the 

 asexually produced spores, and the plant itself is the oophore. 

 In other Uredineae the life-history is somewhat modified 

 in that asexually produced spores of at least two kinds make 



