// U TCH1N SON— ABIES BA LSA MEA 



467 



Ascomycetes. "The time and degree of the combination of the 

 sexual chromosomes is a variable matter. If the prochromosomes 

 can remain in one nucleus with the double chromosome number, 

 or in two distinct nuclei through part or all of the sporophyte 

 generation, it is also possible that they may combine in one nucleus 

 into bivalent chromosomes, and maintain their identity in this 





Fig. 1 



Diagram A. — An interpretation of fertilization in some animals and in Pinits, 

 according to the accounts heretofore recorded. 



Diagram B. — An interpretation of the phenomena already described: the chro- 

 matin originating from the egg nucleus is shown in solid black, that from the male 

 nucleus is outlined and barred; the argument upon which such an interpretation is 

 based is included in the description given in the text; the facts of spindle formation 

 are also indicated. 



Diagram C. — A copy from Gregoire's (7) "schema de l'interpretation meta- 

 syndetique des tetrades-crois," as found in certain lower animals; compare fig. B. 



condition through the sporophyte generation until a true reduction 

 occurs in spore formation." In the well known case of Cyclops, 

 studied by Haecker, the parental chromosomes do not mingle, but 

 persist as individuals and maintain their separation into two groups 

 through several cell generations after "fertilization." We may 

 consider the union of egg and sperm as consisting of three stages: 

 (1) the two nuclei enter the same cytoplasmic mass; (2) the two 



