90 



FIRST GROUP. — THALLOPHYTES. 



rests for a considerable time and then germinates; the product of germination depends 

 on the supply of nutriment ; if it is placed in a nutrient solution at the moment of 

 germination it produces a mycelium ; otherwise it forms a gonidiophore at once, and 

 its gonidia then produce new mycelia. It both cases the outer wall bursts and the 

 inner protrudes in the form of a tube. 



Brefeld has recently discovered a specially interesting mode of formation of fructifi- 

 cation in Mortierella. This plant has very large gonidiophores, which have their base 

 enveloped in the tissue of the mycelium, and on which thousands of gonidia are formed 

 as in Mucor. In the formation of a zygospore the club-shaped extremities of two 



filaments incline towards one an- 

 other and meet, like the two legs 

 of a pair of forceps. The two 

 sexual cells, which are of unequal 

 size, are cut off from the rest 

 of the mycelium, and their con- 

 tents combine to form a zygospore. 

 At the same time hyphae grow out 

 from the base of the cells support- 

 ing the zygospore and unite with 

 other adjacent branches of the my- 

 celium to envelope the young zygo- 

 spore, and grow as it grows. The 

 zygospore attains considerable di- 

 mensions and compresses the hy- 

 phal tissue which surrounds it, and 

 which grows more dense and com- 

 pact from the branching of the 

 hyphae, till at length it encloses 

 the zygospore in a membranous 

 capsule of woven threads, the out- 

 side of which is still a loose hyphal 

 tissue. The growth of the en- 

 velope comes to an end with the 

 maturity of the zygospore, which 

 has a single wall of cellulose, there 

 being no exosporium or endospo- 

 rium ; the hyphae composing the 

 envelope assume a darker colour 

 and their cell walls become cuti- 

 cularised. The germination of the 

 zygospores has not been observed. 

 The formation of the fructification 

 recalls that of Coleochaete, where 

 too the oospore is surrounded by 

 tubes which shoot forth from the 

 cells bearing the oogonium. 

 The Zygomycetes may be divided in the present state of our knowledge into three 

 sub-divisions, distinguished by the mode of formation of their gonidia. 



a. The Mucorineae, including Mortierella, Clwafiep/iora, and some others. The 

 gonidia are formed in the genus Mucor inside globular sporangia borne on long stalks, 

 and are set free by the bursting or the solution of the frail wall of the capsule ; in 

 Pilobohis the wall is firmer, and parts at the base when the capsule is mature, and is 

 flung away to some distance with the spores. Mjtcor Mucedo is one of the commonest 

 of moulds, and is to be found on fruits, bread, dung, even inside old nuts and apples 



Fig. 55. PiptocephaHs Fieseniaiix. M a piece of the mycelium of Mucor 

 Mucedo. on which the mycehum m m of Piptocephalis lives ; h the haus- 

 toria which have penetrated into the filament ai Mucor ; c a gonidiophore ; 

 r^ the two conjugating branches of the mycelium which form the zygo- 

 spore Z. After Brefeld ; r magn. 300 times, the rest magn. 630 times. 



