MOULD FUNGI 95 



jugation in Mucor mucedo as an illustration of the method, we find that 

 the hyphae of two distinct mycelia, which may be designated as the 

 + and — strains, give rise to lateral club-shaped branches. The tips 

 of these two branches (progametes) come into contact and a terminal 

 cell (gamete) is cut oflF from each branch respectively by a transverse 

 wall. The double partition wall is dissolved away by an enzyme, and 

 the two cells coalesce, their nuclei uniting in pairs. A zygospore, is 

 formed, as a resting spore (Figs. 28, 30 and 2,i)- It becomes covered 

 with a thick, warty brown coat. The zygote (zygospore) germinates 

 after a period of rest producing at once, because of the concentrated 

 foods it contains, a sporangiophore bearing a terminal sporangium with 

 sporangiospores. Sometimes the gametes fail to unite through some 

 check to the normal conjugation and the two gametes may then round 

 off and form thick- walled azygospores, and the size of these azygospores 

 depends upon the size of the gametes from which they develop. Blakes- 

 lee has discovered that for the production of zygospores in heterothallic 

 moulds the contact of the hyphae of two distinct mycelia designated 

 + and — are essential. If two — races or two -|- races meet, there 

 is no result. In the homothallic moulds, the two conjugating gametes 

 may arise from the same mycelium. Where the -f- race of one species 

 of mould meets the — race of another species imperfect "hybrids" are 

 formed. The testing out, maleness or femaleness, of the different races 

 is made possible by growing in proximity different kinds of moulds, 

 where a reaction occurs and imperfect hybrids are formed one race 

 must be plus and the other minus. Where the hermaphrodite forms are 

 grown, it is noticed that one gamete is larger and the other smaller, and 

 it is assumed, that the larger gamete is female and the smaller one male. 

 The race of dioecious Mucors, designated tentatively (+), shows a 

 sexual reaction with the smaller or male gamete, while the ( — ) or 

 vegetatively less vigorous race shows a reaction with the larger or 

 female gamete. It is inferred that the -f race of dioecious mucors is 

 female and the — race, male. 



The immediate stimulus to the formation of the progametes prob- 

 ably lies in the contact of hyphae from different strains through the 

 osmotic activity of the hyphal contents. For this reason progametes 

 fail to form in relatively dry air. By suspending two small bags filled 

 with bread soaked in dilute orange juice and inoculated with mould 

 spores, any influence which the substratum might show is eliminated. 



