564 Davis . — Cy to logical Studies on Oenothera . /. 
It is clear that the homotypic mitosis is an equation division distribut- 
ing the halves of the seven sporophytic chromosomes that are separated 
from a similar set by the heterotypic mitosis. These seven sporophytic 
chromosomes become divided lengthwise during anaphase of the heterotypic 
mitosis, and the halves remain closely associated to form seven split chromo- 
somes, which may be followed through the period of interkinesis between 
the heterotypic and homotypic mitoses. 
Cytological Discussion. 
As stated before, three investigators have within recent months 
published the results of cytological studies on Oenothera Lamar ckiana 
or certain of its derivatives. 
Miss Anne M. Lutz has made extensive chromosome counts chiefly 
from studies of root tips, and reports some interesting variations from 
the numbers typical of the genus, which all authors agree are fourteen 
chromosomes for the sporophyte and seven for the f gametophyte. The 
most remarkable exception is found in O. gigas which presents twenty- 
eight chromosomes in the sporophyte. It is to be hoped that her papers, 
largely in the nature of preliminary announcements, 1 will soon be followed 
by detailed accounts with figures. 
Geerts has published preliminary notes on a lengthy study of O . La- 
marckiana , 2 which include an investigation of the embryo sac as well as of 
pollen formation. A full account of his conclusions, to be accompanied 
by figures may be expected in the Recueil des Travaux Botaniques 
Neerlandais. The absence of figures in his preliminary papers makes 
a close comparison of his results and those of the present paper difficult, 
and I shall postpone for the present their consideration. 
Gates has studied the processes of pollen formation in O. Lamar ckiana 
and several of its derivatives, and reported the results in a number of notes 3 
and in two illustrated papers (Gates, ’07 and ’08). The last of the two 
illustrated papers (Gates, ’08) gives his cytological conclusions based chiefly 
on an investigation of O. rubrinervis . I shall not, however, discuss these in 
relation to the present study of O. grandijiora until I have had an opportu- 
nity myself to study O. Lamarckiana or some of its relatives. The results 
of Gates’s investigation of O. rubrinervis , as presented in his last paper, differ 
from those here recorded in a number of important particulars, the chief of 
which are as follows : — 
1 . Following synapsis, Gates describes and figures a thick spirem 
which may be traced continuously for considerable lengths in the nuclear 
1 Science, 1907, p. 151 ; 1908, p. 335 ; 1909, p. 363. 
2 Ber. deut. bot. Gesellsch., 1907, p. 191 ; 1908, p. 608. 
3 Science, 1907, p. 259; 1908, p. 193 and p. 335; 1909, p. 269. 
