282 PROCEEDINGS OF THE AMERICAN ACADEMY. 



gametes assume their ultimate form. In M. Mucedo and in the majority 

 of species in which the process is linown, tlie progametes are in contact 

 only at their extremities. In Phycomyces, however, they grow for a 

 considerable distance more or less intimately adherent with interdigita- 

 tion of their convoluted lobes, and at this stage form stout yellowish 

 pillars, projecting from the substratum (Figure 48). By the more 

 rapid elongation of the subterminal portion, a separation of the individual 

 components finally occurs below their extremities (Figure 49), but, as 

 is the case in all other forms in which the process has been carefully 

 followed, the ends of the progametes are in contact from the very out- 

 set, and never become separate at any stage of their development. The 

 production of the two gametes (Figure 50), and their union to form a 

 zygote, which, by the absorption of nourishment through the suspensors, 

 assumes the form of the mature zygospore, is essentially the same as has 

 been already described in M. Mucedo. At about the time of the dis- 

 solution of the wall between the uniting cells, outgrowths arise from one 

 or both of the suspensors near their junction with the gametes (Figure 50), 

 and, by their elongation and repeated dichotomy, surround the mature 

 zygospore with a loose envelope of forked spines. Septation in the 

 suspensors or in the afferent hyphae may occur as the z^'gospore matures, 

 and is also very generally found in arrested stages of development 

 (Figure 49). 



The adherence of the basal portions of the progametes is probably 

 due to the fact that the mycelial hyphae are firmly imbedded in the sub- 

 stratum, and their separation by the growth of their gametes is therefore 

 prevented. The presence of a curvature in the progamete of Spinellus 

 when their points of origin are closely adjacent, renders it possible that 

 such a curvature in Phycomyces is also a matter of no great significance 

 and connected merely with the fixed position of the conjugative hyphae. 

 The condition is frequently more simple than is shown in Figure 48, 

 and cases have been observed in which the bases of the suspensors are 

 simply crossed with little or no development of interlocking lobes. 



Under the somewhat unfavorable conditions which exist in cell cul- 

 tures, progametes are not produced at the places of contact between 

 all of the sexually opposite hyphae of the two mycelia, and apparently 

 the quantity of available nutriment has much influence in determining 

 whether a single system of mycelial branches will take part in the 

 formation of more than one zygospore. 



The continued growth and branching of the apposed (+) and (— ) 

 mvcelia would ultimately bring sexually opposite hyphae into contact. 



