26 BOTANICAL GAZETTE [January 



the internal constitution, which causes the mass mutation, is not 

 in itself a cause for further mutability. 



8. The constitution of the gametes of 0. rubrinervis can directly 

 be proven by a cross with O. deserens, since O. rubrinervis = {deserens 

 -\-velutina)xO. deserens produces 0. deserens and (O. deserens X 

 velutina) or rubrinervis. 



g. Crosses of O. rubrinervis with 0. Lamarckiana give three 

 types of hybrids, besides about one-fourth empty seeds. One 

 type exactly resembles 0. Lamarckiana and is constant in its pro- 

 geny. A second type called lucida has broader and more shiny 

 leaves, and after self-fertilization splits off brittle specimens. The 

 third type is either subrobusta or rubrinervis, and in the first case 

 may produce the brittle form in the second generation. All these 

 phenomena are easily explained by the proposed formula for the 

 constitution of O. rubrinervis as a half mutant. They were con- 

 firmed by means of crosses with O. nanella and some other mutants. 



10. O. oblonga is quite analogous to O. rubrinervis, since it must 

 arise through a mutation of the typical sexual cells of 0. Lamarcki- 

 ana, leaving the velutina gametes unchanged. Contrary to O. ru- 

 brinervis, however, the two lethal factors remain in their condition, 

 and moreover the mutated gametes must be assumed to become 

 suppressed in the pollen of the mutant. 



11. 0. nanella seems to arise through mutations in the velutina 

 gametes of O. Lamarckiana, since after crosses with other species or 

 mutants it is not split off by the laeta hybrids, but only by those of 

 the type velutina. 



LuNTEREN, Holland 



