230 INTRODUCTION TO THE STUDY OF FUNGI 



soon dissolved, so that the contents coalesce, and a single cell is 

 constituted from the union of the two gametes, which is, in 

 effect, the young zygospore. Henceforward the cell-wall of 

 the zygospore becomes thickened, and coloured, so that it 

 usually acquires a brown colour, and is warted or spinulose 

 when mature. The zygospores thus formed are also character- 

 ised as resting spores, because they are capable of resting, or 

 remaining in a dormant condition for months before germina- 

 tion takes place, usually through the winter, becoming active 

 in the spring. 



It' may sometimes happen that the two gametes, instead of 

 coalescing, remain distinct ; or in rare cases only one archicarp 

 is produced; yet in such instances a body resembling a 

 zygospore is developed, without conjugation, and therefore the 

 resultant spore is called an azygospore. In some species the 

 zygospores are produced freely, and in considerable number, 

 amongst the ordinary vegetative hyphae, at the same time, or 

 succeeding, the production of the ordinary gonidia ; but the 

 latter germinate at once, without any period of rest, and 

 hence they do not survive through the winter. Usually the 

 development of gonidia is arrested in the autumn and the 

 formation of zygospores commences. In the absence of 

 zygospores the mycelium becomes perennial, and thus survives 

 the winter, so that the species may be perpetuated Provision 

 is thus made for reproduction, asexually, by means of gonidia, 

 which germinate at once ; by azygospores, which germinate 

 after a period of rest, and sometimes by a perennial mycelium, 

 which survives the winter ; and sexually by the production of 

 zygospores, which accrue from the conjugation of two approxi- 

 mating specialised branches of the hyphae. 



The Peronosporaceae are, in their typical forms, more nearly 

 resembling the Muce&ines in habit than are the Mucoraceae. 

 The erect hyphae, or gonidiophores, are usually furcately 

 branched two or three times, and bear the gonidia (Fig. 106), as 

 more or less elliptical hyaline bodies, at the ends of the branches. 

 These constitute the means of asexual reproduction, and may 

 be developed successively or simultaneously; In some cases 

 the gonidia so produced appear to be simple gonidia, but in 

 others they undergo transformation ; in the former case they 



