962 Davis.—A Comparison of the Reduction Divisions of 
(assuming Lamarckiana to be of hybrid origin) than from Lamarckiana 
itself. Furthermore, the trend of evolution ingigas is distinctly progressive 
as far as evidence is furnished by the greater size of its organs and vegeta¬ 
tive vigour. There is apparently none of the retrogressive variation so 
conspicuously shown in almost all of de Vries’ ‘ mutants 5 in which one 
or more characters of Lamarckiana have dropped out or are presented 
in reduced form in the ‘ mutants ’. The remarkable rarity of gigas as a 
derivative from Lamarckiana should not, however, be forgotten in the 
acceptance of its being representative of a true mutant. 
Cytological Discussion. 
Including the results presented in this paper, the writer has published 
accounts of the reduction divisions in four species of Oenothera , viz.: 
grandijlora (Davis, ’ 09 ), biennis (Davis, TO), Lamarckiana , and gigas. The 
material of the last three species was from strains that had been bred in 
‘ pure lines ’ for two or more generations ; the material of grandijlora was 
from plants grown from wild seeds. In addition to these species the history 
of the reduction divisions of O . muricata has also been traced, but this 
history agrees so closely with the account of biennis that a description 
would be scarcely more than repetition. From these studies we are perhaps 
in a position to take a general survey of the conditions presented by the 
Oenotheras in relation to certain problems of cytology. It is, however, 
probable that important evidence on some of the chief difficulties will 
come from the investigation of certain Oenothera hybrids which will be 
the next step in the writer’s studies, and this brief review must be, there¬ 
fore, somewhat tentative in character. 
The attention which in recent years has been devoted to the study 
of the chromosome history during interkinesis is rapidly giving important 
results. The work of Overton (’ 05 , ’ 09 ), Rosenberg (’ 04 , ’ 05 , ’ 09 ), and 
Lundegard (’ 09 , TO) upon a variety of plants has placed the prochromo¬ 
some theory in a strong position. The last statement of this view by 
Overton (Science, vol. xxxiii, 1911, p. 193) reports that the chromo¬ 
somes following a mitosis form by alveolization independent reticula in 
the resting nucleus which touch one another but do not anastomose, and 
which during the prophase of mitosis by condensation become again trans¬ 
formed into chromosomes. My studies on Oenothera seem to favour the 
above view, although I have as yet been unable to trace the outlines of 
the chromosome reticula in the mid-period of the resting nucleus. The 
chromosomes may readily be followed in the process of alveolization for 
a considerable time following the mitosis and chromatic bodies, or pro¬ 
chromosomes, may be recognized at a stage during the organization of the 
dense chromatic network which precedes the differentiation of the spireme, 
when their boundaries again become lost. There is, however, a mid-period 
