298 Non-Isolable Races. 
the occurrence of bolters is considerably diminished ; in 
one experiment for instance from 7 to 4 c /o. 1 Other 
results point in the same direction. 
HEUZE, in his valuable little book on the oil plants, 2 
says with regard to the rape (Brassica Napus oleifem), 
that in the north of France it should not be sown before 
the middle of July or after the middle of August, for in 
the latter case the plants will not be strong enough to sur- 
vive the winter, and in the former too large a proportion 
will set seed in the first year. The same thing is true of 
a whole series of other biennial plants both cultivated 
and wild ; those which germinate late become biennial ; 
of those which germinate early a greater portion become 
annual, the earlier the sowing or the germination took 
place. 
In these cases we are not concerned with the induction 
of bolting by night frosts, or by any other stimulus, but 
with a case of inherited variability. It is true that the 
beet possesses this variability also, but the general con- 
ditions in this species are much complicated thereby. 
That we have to deal with a phenomenon of inheritance 
is proved by the fact that the annual form can easily 
be fixed by selection, without, however, attaining a state 
of absolute purity. RIMPAU sowed the seed of bolters, 3 
and by always selecting seeds ripened in the first year, 
he obtained in the fourth generation a race whose seeds 
when sown on the 31st of March produced annual plants 
only and which in the fifth generation, when sown on 
the 5th of April, was as constant an annual as the normal 
RIMPAU, Das Aufschiessen dcr Rimkelrilben, Landwirtsch. 
Jahrbiicher, 1880, p. 192. 
2 L. HEUZE, Les plantes oleagineuses, Bibliotheque du cultivateur, 
Paris, 2d ed., p. 16. 
3 Loc. cit., p. 197. 
