No. 525] SEXUAL BEPBODUCTION IN FUNGI 



539 



The phenomena of conjugate division also indicate very 

 clearly how the mechanism of karyokinesis, including 

 centrosomes, asters and spindles, may he partly or wholly 

 combined in a single system without necessitating a sim- 

 ilar union of the idioplasmic units. 



One of the most important points in this sexual process 

 in the rusts is that the nuclei do finally fuse in the teleu- 

 tospore. One might suppose that since the nuclei can 

 function as physically independent units through the 

 whole life of the sporophyte with its manifold vegetative 

 and reproductive phases, a reduction division might be 

 accomplished by the mere insertion of a wall between the 

 conjugate nuclei. This may be what occurs in Endo- 

 phyllum according to Maire. Still the fact that the 

 nuclei fuse before the heterotypic division in practically 

 all other rusts is certainly strongly suggestive that 

 synapsis and its accompanying phases represent a stage 

 of mutual influence if not of interchange of physical ma- 

 terial between the chromosomes much more intimate than 

 any which has preceded it in the life of the sporophyte. 



On the other hand, it is plain that the nuclear fusion 

 is unnecessary so far as the sporophyte itself is con- 

 cerned. The sporophyte of the rusts, as in other plants, 

 is the distinctively dominant and progressive phase in 

 the life cycle of the fungus. The uredo mycelium and the 

 rapid succession of crops of uredospores with all their 

 adaptations for rapid spread and virulent development 

 are a parallel in every respect to the sporophyte in every 

 type of plant in which it is found from the ferns to the 

 seed plants. It is plain then that the vigor and adapta- 

 bility of the sporophyte are not dependent upon the com- 

 bination of the sets of parental chromosomes in a single 

 nucleus. The same results are possible with two more or 

 less independent nuclei in the cell, each containing the 

 chromosomes from one parent. 



For the ascomycetes Dangeard extended Wager's ob- 

 servation of endokaryogamy in the basidium by the dis- 



