PYRONEMA. 115 



pass at once into the oogonium, to the central mass of egg-nuclei, and 

 become mingled with them (Fig. 43, F). The number of male nuclei 

 entering the oogonium does not seem to be exactly the same as the 

 number of egg-nuclei to be fecundated. Both sexual organs arise as 

 multinucleate cells, and, as there is no evidence subsequently of a 

 parallel series of nuclear divisions in each, it is difficult to see how 

 exactly the same number could be provided in each organ. 



Only a small portion of the cytoplasm of the antheridium passes 

 into the egg-cell, so that here, as elsewhere in the plant kingdom, the 

 superior significance of the nuclei in fecundation is strikingly mani- 

 fested. The male and female nuclei mingled in the central group are 

 indistinguishable in size, structure, and staining qualities, so that it is 



FIG 43. Fusion of sexual nuclei in the oogonium of Pyronema. (After Harper.) 



F, basal wall of trichogyne dissolved, male and female nuclei collected in dense mass 



in center of oSgonium and fusing in pairs ; nuclei still present in trichogyne alid 

 upper end of antheridium ; ascogenous hyphae budding out from oogonium. 



G, group effusing nuclei from central mass of nuclei in an oogonium. 



impossible to pick out a single nucleus and say whether it has come 

 from the oogonium or antheridium. The nuclei fuse in pairs while 

 they are aggregated in the dense mass (Fig. 43, G). The behavior 

 of all the nuclei in the center of the mass was not determined with 

 certainty, but there is every reason to believe that the rule of fusion 

 in pairs holds for nearly the whole mass. Harper expressly states that 

 there is no general fusion of the nuclei into a single mass, as can be 

 clearly seen when the nuclei scatter after fusion. 



The oogonium of Pyronema functions at once as an ascogonium. 

 All fecundated nuclei pass into ascogenous hyphse and may reach the 

 Here the young ascus develops also from the penultimate cell 



asci. 



of a bent ascogenous hypha, and in it two nuclei are present which 



