BLASTOCLADIALES 617 



of different species is much slower. Hatch (1938) assumed that age 

 plays a part in determining whether fusion will take place. He asserts 

 that it is achieved most readily between recently emerged gametes, but 

 becomes increasingly difficult as time elapses. Conjugation most fre- 

 quently occurs when either one or both of the gametes is temporarily 

 quiescent or exhibiting amoeboid movement. Actual fusion is preceded 

 by a more or less protracted period of intense pseudopodial activity on 

 the part of both gametes. During this period the plasma of the two 

 often becomes strongly vacuolate, and the flagella may wave feebly. 

 Eventually, more or less complete fusion takes place, after which the 

 zygote swims vigorously about for a time or undergoes a period of 

 amoeboid movement before coming permanently to rest. It then rounds 

 off and encysts; the flagella (according to Hatch, op. cit.) are dehisced; 

 germination then ensues. Cytological investigations by Hatch (op. cit.) 

 of stages in the fusion of the gametes indicate that actual fusion takes 

 place only when the flagella-bearing ends are in opposition. This obser- 

 vation may explain, at least in part, the often prolonged preliminary 

 amoeboid activity. Hatch did not believe that the male plasma is engulf- 

 ed by that of the female but, rather, that both empty toward a common 

 point of rupture to form the new zygote. He found that nuclear fusion 

 does not occur in most instances until after the flagella of the zygote 

 are cast off and the nuclear caps have dissociated, that is, at the time 

 of germination (Fig. 41 R-V, p. 622). Fused nuclei were seen in zygotes 

 which still bore their flagella. This, Hatch thought, can be explained 



Explanation of Figure 40 



A. Allomyces arbuscula E. J. Butler, tip of hypha of gametangial plant 

 bearing terminal colorless female gametangia and subterminal golden-orange 

 male gametangia. B. Allomyces javanicus Kniep, tip of hypha of gametangial 

 plant bearing a terminal golden-orange male gametangium and a subterminal 

 colorless female one. C. Allomyces macrogynus (Emerson) Emerson and 

 Wilson, male and female gametes being discharged and conjugating. D-E. 

 Allomyces anomalus Emerson; D, hypha bearing resting spores; £, zoospo- 

 rangia, the terminal one discharging zoospores. F-G. Allomyces moniliformis 

 Coker and Braxton: F, tip of hypha bearing discharged zoosporangium. 

 terminal immature resting spore, and, at base, a mature beaked one; G, 

 empty basipetal zoosporangia and discharging one. 



(Sparrow, 1943) 



