126 THE THEORY OF THE GENE 



the spores (Fig. 78). Pieces of the sporophyte if kept 

 under moist conditions give rise to threads whose cells 

 are diploid. These become a true protonema that gives 

 rise in time to diploid eggs and diploid sperm-cells. By 

 the union of these germ-cells tetraploid sporophyte 

 plants are formed (Fig. 79). Here the normal haploids 

 have been duplicated by a diploid protonema and moss 

 plant, and the diploid sporophyte has been duplicated by 

 a tetraploid sporophyte. 



The March als have made comparative measurements 

 of the size of the cells of the normal plants and of those 

 of the tetraploids. In three species the volume of the 

 normal perianth cells to that of the doubles was found to 

 be as 1 to 2.3 ; 1 to 1.8 ; and 1 to 2. The volumes of the cells 

 of the normal antheridia in the two types were as 1 to 1.8 

 and those of the nuclei were about as 1 to 2. The egg-cells 

 were as 1 to 1.9. Measurements of the antheridial organs 

 (that carry the sperm-cells) and of the archegonial 

 organs (that carry the egg) showed in all cases that 

 the double types are longer and broader than are the 

 normal types. It is evident that the increase in size of 

 the double types is due to larger cells and these in turn 

 have larger nuclei, which, other evidence has shown, 

 have in the double types twice as many chromosomes as 

 in the normal type. This was, of course, to be expected 

 from their origin by regeneration from the normal sporo- 

 phyte. 



in the sporophyte generation the mother cells of the 2n 

 spores were to those of the 4n spores about as 1 to 2. 



The two maturation divisions in mosses, i.e., the divi- 

 sions following conjugation of the chromosomes, take 

 place in the sporophyte at the time when the spores are 

 formed— four from each spore mother cell. If, in mosses, 

 the chromosomes carry the genes, the doubling of the 

 chromosomes (tetraploid) in double types is expected to 



