CHAPTER V. — COMPARATIVE REVIEW. —MUCORINI. 147 



mycelium which displays the characters and follows the course of development here 

 described. Hence a regular alternation of generations is observed in the life-history 

 of these plants; typical gonidiophores are formed directly and normally from the 

 germinating zygospore, and their products germinate and form a mycelium which 

 produces gonidia again and ultimately zygospores. This course of development may, 

 ikis true, be so far disturbed, that the germ-tube which proceeds from the zygospores, 

 if ft is hindered from forming gonidia directly but is well supplied with food, as when 

 it is artificially sunk for instance beneath the surface of a nutrient solution, may 

 develope into a mycelium which does not become sporiferous till after the lapse of 

 some time ; but this fact does not alter our determination of what is the normal 

 behaviour of these plants. No other phenomena of regular alternation of 

 generations have been observed; I have seen indeed the mycelium formed from 

 gonidia produce zygospores first and then gonidiophores in Sporodinia grandis, the 

 species which most frequently produces zygospores and grows on fleshy Hyme- 

 nomycetes ; but the reverse order of events is quite as common, and sometimes no 

 zygospores are formed at all. The mycelium developed from zygospores may in 

 this species produce zygospores directly, omitting the formation of gonidia \ 



In all other known species the formation of zygospores is always preceded 

 by a copious development of gonidia on the same mycelium, and most specimens 

 never get further than the gonidia. It may be a question therefore whether possibly 

 a generation forming zygospores succeeds with some regularity to a large number 

 of successive generations which only form gonidia ; experiments in artificial cultivation 

 have only given negative answers 2 . 



Section XLII. The formation of zygospores is known only in the smaller 

 number of species, but these belong to almost all the chief genera of the group. 

 It begins in the case of each zygospore with the appearance of a pair of archicarps 

 (section XXXIII), and these are formed in Sporodinia on special erect dicho- 

 tomously branching hyphae resembling the sporangiophores ; in all other known 

 cases they appear singly on sporangiophores (Chaetocladium, Absidia), or as im- 

 mediate branches of the mycelium spread in or on the substratum ; the latter case 

 occurs also in Sporodinia, if the drawing in the vignette which precedes the tables in 

 Tulasne's Carpologia is correct. The archicarps in each pair spring either from 

 spots in the hyphae which are morphologically close to one another, as in Phy- 

 comyces 3 and Sporodinia 4 , or from spots which are only locally adjoining, places 

 of contact of branches of morphologically remote e?igin, as in Piptocephalis 5 and 

 Mucor stolonifer 6 . Both conditions of origin c6rfe*spond to those which have been 

 described for the antheridia and oogonia of the Peronosporeae and Saprolegnieae, 

 and appear as in them to vary from species to species and in individuals of the same 

 species. The archicarps of a pair (Fig. 72 a, b) are small branches of the hyphae, 



1 Brefeld in Sitzgsber. d. Ges. naturf. Freunde z. Berlin, 15 Juli, 1875, 



2 Brefeld, Schimmelpilze, IV. 



3 Van Tieghem, I, t. 20, Fig. 4. 



4 De Bary, Beitr. I. 



6 Brefeld, Schimmelpilze, I, p. 48. 



6 De Bary, Beitr. II. 



L 2 



