404 
Cooperative Investigations on Plants 
the real fact of the case being that these species or characters are being subjected 
to very different intensities of selection. 
If the distribution of the character be approximately normal, and if /u, be the 
ratio of the variability of selected parents to the variability of the general popula- 
tion for a given character, then it is known that the true value of inheritance r is 
closely given by : 
Thus with anything like stringency of selection p may be quite small, and the 
value of r completely screened. We may illustrate this on various characters. 
(a) Stigmata. In the case of a crop under very favourable conditions, or 
where every plant is separately grown as at Oxford, we have a high variability, 
amounting to 2 or over. But at Parkstone the actual variability was only 1'56, 
and on a random selection of 129 seed capsules from this crop only 92 sets 
germinated at Crewe, and of these sets the maternal plants had a stigmatic band 
variability of 1-4590. Thus /Lt=-7295 for the stringency of selection of the 
maternal plants at Crewe, as compared with Shirley Poppies at large. 
{h) Extent of Margin. If we take the 971 plants at Parkstone and the 408 
offspring at Crewe from certain of them we note the following distributions 
(see p. 417): 
h 
6s 
s 
sn 
n 
Totals 
Parkstone General Population 
52 
73 
84 
71 
691 
971 
Parkstone ]\Iothers of Crewe Daughters . . . 
1 
58 
64 
10 
275 
408 
Or, dividing into three groups, we have the percentages : 
Broad Margins 
Slight Margins 
Insignificant 
General Population ... 
Mother Plants 
12-9 
14-5 
8-7 
15-7 
78-4 
69-8 
We see that there has been a considerable alteration in the distribution of 
margins, between the actual mothers and the general population from which they 
were selected at random. Let us treat the distribution of margin as approximately 
normal to get some idea of the stringency of selection. In this case if d be the 
range of margins classed by this one observer as slight we find, if a be the 
standard deviation of the general Parkstone population and a' that of the selected 
mothers : 
= -34400- and c^=-5497o-'. 
Hence ^ = a'ja = -02589. 
