418 



THE AM ERIC AX NATURALIST. [Vol. XXXV II. 



the chromatin network is very much contracted, a very con- 

 spicuous condition which is not well understood. The first 

 nuclear division in the spore mother cell presents the gametophyte 

 number of chromosomes and this is followed by a second divi- 

 sion so that four nuclei result, each of which is destined to 

 preside over a spore. 



The fact that the number of spores formed in each mother 

 cell is four appears to have no important morphological signifi- 

 cance. It has no connection with reduction phenomena which, as 

 explained above, take place before these divisions. Among the 

 seed plants this division is very frequently omitted in the mega 

 spore mother cells which give rise directly to the gametophyte 

 (embryo sac) thus cutting out a portion of the usual history in 



However the fact that four spores are formed in each spore 

 mother cell is interesting because almost universal among the 



mation in the Spermatophytes. We can see no reason why the 

 number should be four nor is any light thrown upon the prob- 

 lem from our knowledge of the thallophytes. 



To summarize this explanation of the sporophyte ; we assume 



formed spore a different mechanism from the parent gametophyte 



during the sporophyte. The result is a differentiation of the 



(somatic) in contrast to the reproductive tissue which is propor- 

 tionally reduced in quantity. The latter (archesporium) gener- 

 ally appears at certain periods of development and in definite 

 regions and represents the return of the sporophytic plasm to the 

 potentialities of the gametophyte. We do not mean to imply 

 that the entire development of the sporophyte 



