162 Humbert. 
evolution, or the value_of the study of variation. Any biological 
bibliography will list numerous papers on these subjects. Neither is 
it necessary to defend the use of the statistical method as a biological 
tool. More and more it is being recognized as the surest means of 
registering progress in the experimental laboratory. 
The plant used, Silene noctiflora, is a wild species of no economic 
value. It has several qualities which adapt it to a study of this 
kind; (r) it has not been altered by domestication as have our economic 
plants; (2) it produces a great abundance of viable seed thus per- 
mitting very rapid multiplication of the lines; (3) the seeds are borne 
in a capsule so that for injection work many seeds may be affected 
by one injection; (4) after reaching a certain stage of maturity the 
plants remain for some time unchanged, so that a large number may 
be measured under very similar conditions. For instance, the height, 
width, and number of branches remain unchanged and the seed pods 
persist. 
While it would of course be desirable in many ways to use an 
economic crop in a study of this kind, the requirements of the out- 
lined study made such a choice impossible. 
Before discussing the four separate problems mentioned above, 
we shall consister somewhat in detail the matevials and methods used 
in the investigation. 
Materials and methods. 
Seeds for this study were collected from an isolated plant in the 
summer of 1907. This (grandmother) plant was given the pedigree 
number 250 and all later pedigree numbers refer back to this plant. 
In the early spring of 1908 twentyseven seeds were started in steri- 
lized pots of soil and later transplanted to the ,,Breeding Garden.‘ 
The (mother) plants produced were numbered, according to the system 
outlined in „Plant Breeding‘, by Dr. H. J. Webber’), 250—1, 
250—2, 250—3,..... , 250—27 and received identical culture and 
environmental conditions so far as these conditions are under the 
control of any experimenter. 
A number of flower buds on each of these twentyseven plants 
were covered with paper bags to insure self fertilization. Certain of 
the buds under bag were then injected with chemicals and rebaged. 
Others were left untreated to be used as checks and in other ex- 
1) Bailey, L. H. Plant Breeding, pp 308—319. (Macmillan Co. N. Y. 1906.) 
