No. 525] SEXUAL REPRODUCTION IN FUNGI 545 



the assumption that the appearance of binucleated cells 

 and possibly conjugate division in the ascogenous cells of 

 the discomycetes mentioned above indicate not the per- 

 sistence of unfused but paired gametic nuclei, but a work- 

 ing back of conjugate division from the spore mother cell 

 into the tissues of the sporophyte, thus giving gradually 

 to the endokaryogamy in the ascus more and more of a 

 sexual significance. 



The evidence has accumulated in many lines that in 

 several groups of the fungi the sexual process is fol- 

 lowed by a longer or shorter period of development with 

 cells containing a double chromosome number. Evi- 

 dence from a direct counting of the chromosomes before 

 and after fusion is lacking, owing to the small size of 

 the nuclei, still there can be no reasonable doubt that the 

 regularly binucleated cells of the rusts which form an 

 unbroken series from the aecidium to the teleutospore 

 contain twice the number of chromosomes present in 

 the uninucleated mycelial cells from which the aecidium 

 arises. As already noted, the conditions in the rusts are 

 especially favorable for demonstrating that the sexual 

 fusion inaugurates a period of development with cells 

 containing 2n chromosomes and that this sporophytic 

 stage tends to predominate in the life cycle both as to 

 length and complexity. 



It is quite evident also in advance of a knowledge of 

 the complete etiological data that the double division 

 involved in forming the promycelial cells is to be con- 

 sidered as a reduction period. 



In the smuts and Basidiomycetes the limits of the 

 garnet ophyte and sporophyte are not so definitely marked 

 as in the rusts, but the binucleated phase is certainly to 

 be regarded as sporophytic however it may be inaugu- 

 rated. In the Ascomycetes the morphological relations 

 of the mycelium and ascocarp have long been regarded 

 as showing a parallelism with the conditions in liver- 

 worts and mosses. The fact of a triple division in the 

 ascus in contrast with the elsewhere universally present 



