196 Humbert. 
250—7 and 250—11 shows this very plainly. Also that the same 
chemical does not produce an equal effect each time, even when used 
on the same plant. This may indicate differences in the condition 
of the buds at the time of treatment. 
We may conclude that while the injection of chemical stimulants 
in the developing ovary did not, in the case of Silene noctiflora, 
produce mutations, such injections did produce in most cases a marked 
increase in the variability of the species. This change would be 
somewhat more strongly brought out were the lines of equal size and 
only the standard deviation used as the measure. In all cases the 
number of variates in the lines from injected capsules is less than 
lines from the uninjected. 
II. Effectiveness of Selection in pure lines. 
The question as to whether or not accumulative effects accrue 
from continued selection has long occupied an important place in 
discussions of inheritance. The general belief that mass selection is 
the surest if not the only method of improvement is shown over and 
over again by the practices of both practical breeders and experiment 
station workers. ‘‘Select the best and use this for the parent stock 
with the assurance that ‘like produces like’”, has been the gist of 
counsel. Darwin!) was firmly of the opinion that improvement has 
been brought about chiefly by the piling up of small favorable fluc- 
tuations and says, “We cannot suppose that all breeds were suddenly 
produced as perfect and as useful as we now see them, indeed in 
many cases we know that this has not been their history. The key 
is man’s power of accumulative selection; nature gives successive 
variations; man adds them up in certain directions useful to him. 
If selection consisted merely in separating some very distinct variety 
and breeding from it, the principle would be so obvious as hardly 
to be worth notice; but its importance consists in the great effect 
produced by the accumulation in one direction, during successive 
generations, of differences absolutely inappreciable by an uneducated 
Bye. 20... 
Those who believe that accumulative effects do result from con- 
tinued selection have had a strong champion in the statistical school. 
Galton’s?) law of ancestral inheritance (somewhat modified by 
1) Darwin, Chas., Origin of Species. Chap. I. pp 25—26. 
2) Galton, Francis. Natural inheritance. 1389. 
