iQisl 



BARTLETT—MASS MUTATION 



441 



varying degrees of mutability. The progenies of crosses indicate 

 that mass mutability is conditioned by the female gametes. 



Mut. latifolia. — In contrast with mut. angustij'olia, mut. latifolia 

 reproduces itself in part of its progeny. Its descendants include 

 roughly 50 per cent f. typica and 50 per cent mut. latifolia, the 

 proportion varying within rather wide limits. Moreover, mut. 

 latifolia gives progenies of the same type whether self-pollinated or 



Fig. 7. — Mut. setacea: 2 mature plants from the Fa progeny of f. typica, from F, 

 parent Lexington E-5; the right-hand plant, Lexington E-5-164, is sho^\Ti also in fig. 5; 

 note particularly the dimorphic foliage. 



cross-pollinated with f. typica. The reciprocal cross, with f. typica 



as the pistillate parent, consists only of f. typica, aside from the 



usual low proportion of mutations, among which mut. latifolia may 



or may not happen to occur. These relations are as follows: 



mut. latifoliaXnxat. latifolia-^ i. typica-\-m.ut. latifolia 

 mut. latifoliaXi- typica-^ f. typica-\-rrmt. latifolia 

 f. typicaXraxxt. latifolia-^ f. typica 



