146 



DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



zygospores, these organs have never yet been observed ; and since some of the species 



have been frequently and carefully examined, it may perhaps be conjectured that they 



do not at present produce zygospores, but only gonidia. 



The members of the group of Mucorini, with the exception of the doubtful 



genus Zygochytrium, which will be considered in a later page, are plants of the dry 



land, and grow most of them on dead organic bodies (especially animal excrements), 



some being parasitic on other Mucorini. 



A spore gives rise to a mycelium having the form of a much-branched unicellular 



tube, as may be seen most readily by cultivating the plant in drops of fluid or in 



mucilage on a microscopic 

 slide (Fig. 71 ), and it 

 is not until gonidiophores 

 begin to be produced that 

 the tube is in a condition to 

 form the transverse septa 

 which then usually appear in 

 it. The typical gonidiophores 

 (Fig. 71 g) begin after one 

 or more days' time to shoot 

 upwards from the mycelium 

 which has spread in the 

 substratum ; they appear in 

 the form of branches which 

 are usually erect, and, like 

 the parent-tube, are at first 

 without transverse septa. In 

 some species, as Mortierella 

 and Syncephalis, they are al- 

 most microscopically small ; 

 in most cases, however, they 

 are of considerable size, from 

 one to several centimetres 

 in length, in Phycomyces 

 10-30 cm. Older or im- 

 perfectly nourished mycelia 

 may subsequently produce 

 a fresh crop of accessory 



FIG 71. B. Phycomyces nittm. Plants three days old grown from a gonidium in -J- 1 f "D ' 11 



gelatine with decoction of plums; the mycelium has spread horizontally,^- a gonidio- gOmdial JOmiS. l>Ut in all 

 phore. A, C, D Afucor MitCftfo highly magnified. A sporangium in optical longitu- . . . , . , 



dinal section. In C the germinating zygospore .z is borne on suspensors; K germ-tube, SpCClCS WhlCIl haVC bCCH 

 S sporangium. D conjugation ; aa gametes, M suspensors. B slightly, A, C and D more , , , j i_ 



highly magnified. After Brefeld from Sachs' Lehrbuch. thoroughly examined the 



mycelium under favourable 



circumstances completes its development by forming zygospores. Finally the 

 ripe zygospore, after remaining dormant for several months, puts out one or 

 more strong germ-tubes, which develope at once without mycelial formation 

 into the typical gonidiophores which are characteristic of the species (Fig. 71 C). 

 The gonidia of every species invariably produce, if the conditions are suitable, a 



