152 



PHYSICAL BASIS OF HEREDITY 



the number to l^V. It is at this time, too, in mosses with 

 separate sexes, that sex differentiation takes place, for as 

 the Marchals have shown, each spore gives rise to a male 



xm) 



x(n) 



< 



-f 



y{2Tl) Sporophyte 



X^Td Gametophyte 



© 1/(71) 



©xm) 



Fig. 59. — Life cycle of moss. The mycelial thread and the moss plant constitute 

 the In, or gametophyte generation; and the stalk and capsule (with its contained spores), 

 arising after fertilization out of the moss plant, constitutes the £n or sporophyte generation. 



or to a female thread that produces archegonia or else 

 antheridia regardless of the condition under which the 

 young plants are reared. Allen has recently shown in 

 related plants — the liverworts — that during the reduction 

 division (that gives rise to the spores) an unpaired sex- 



