198 Humbert. 
Jennings?!) in his experiments with the common infusorian Pa- 
ramecium published in 1908, found, as did Johannsen, that from a 
mixed population pure lines may be isolated, which will breed true 
and not revert to the mean of the original population even when 
selection is discontinued. Selection within the pure lines was in- 
effective. 
Pearl?) has recently shown that there is no cumulative effect 
where Domestic Fowls are selected for fecundity. More than this, 
he shows that fowls that are the result of such selection are more 
variable for this character than fowls that are not the result of such 
selection. 
Hanel?) with Hydra, and Love®) with peas, have found the 
same general rcsults to obtain. 
All of these experiments which point to the lack of cumulative 
effect show that all of the experiments usually cited to prove that 
cumulative effects do accrue, are subject to the explanation that the 
results are due to the more or less complete isolation of pure lines 
from a mixed population. 
The work of the author with Silene noctiflora offers some data 
on the subject. By comparing the measurements taken on the mother 
plants (table No. 2) with the means of the lines from untreated cap- 
sules of the next generation (tables Nos. 8, 9, 10 and 11) the following 
curves are produced. Fig. No.1 is for the character “height”, No. 2 
is for “width”, No. 3 “number of branches”, and No. 4 is for the 
character “number of seed pods’. In each case the solid line re- 
presents the measurement of the mother plants, arranged so as to 
form an ascending series, and the broken line represents the mean 
af the corresponding progeny. 
Were there an inheritance of the characters in question between 
mother plants and their progeny the lines would run more or less 
parallel. This they do not do, especially in cases of Fig. 3 (number 
of branches) and Fig. 4 (number of seed pods). In these instances 
the ,,best straight lines‘‘ diverge more and more from each other. 
1) Jennings, H.S. Heredity, Variation, and Evolution in Protozoa. II. Proc. 
Amer. Phil. Soc. 47:393—546. 1908. 
2) Pearl, Raymond. Is there a Cumulative Effect of Selection? Zeitschr. Ind. 
Abstammungs- und Vererbungslehre. Band II. Heft 4. 
3) Hanel, Elise. Vererbung bei ungeschlechtlicher Fortpflanzung von Hydra 
grisea. Jenaische Zeitschr. 43:321—372. 1907. 
4) Love, H. H. Are Fluctations Inherited? American Naturalist. July 1910. 
