82 BOTANICAL GAZETTE [FEBRUARY 
Mr. Gro. M. Gray for aid in planting and caring for the garden. 
These researches are being continued with the aid of a fellowship 
at the University of Chicago, and I am indebted to Professor JOHN 
M. CouLter and Dr. CHARLES J. CHAMBERLAIN for supervision. 
Materials and methods 
The first material of Oenothera lata was collected from a small 
garden of evening primroses at Woods Hole in 1905 from guarded 
seeds of DEVrIES. Stages were preserved for a study of sporogenesis 
and embryo sac development in O. /afa and its hybrid forms; but 
the results recorded here will concern only pollen development, 
as the work on the megaspore and embryo sac has not been com- 
pleted. The study of pollen development was taken up first because 
an interesting problem was presented by the abortion of the pollen, 
and because the reduction divisions in the microspore mother cell 
are for various reasons more easily investigated than those of the 
megaspore mother cell. The possibility of a cytological explanation 
of the segregation of characters in Mendelian hybrids, no one 0 
which has yet been worked out on a chromosome basis, as well as the 
possibility of an explanation of the phenomena of mutation itself 
have also been kept in mind. The work has not yet reached a 
stage where it is possible to say that a cytological explanation for 
the Mendelian segregation of characters will be found, though this 
is possible. Some of the other results which will be described later, 
however, suggest that there may be found in the chromosomes a 
basis for the explanation of discontinuous variation or mutation, the 
suggestion being that the appearance of the mutant is preceded by 
certain morphological changes in the chromatin of the germ cells 
from which it originates, or, more exactly stated, that the germ 
cells from which a mutant arises differ in the structure of their idio- 
plasm from the ordinary germ cells of the parent species. 
Material has also been collected from O. Lamarckiana and several 
other of the mutants for comparison with O. lata. 
The garden of 1906 at Woods Hole contained O. Lamarckiana 
and five of the mutants, all grown from guarded seeds of DEVRIES, 
which were planted in the greenhouse at the University of Chicago, 
the young seedlings being transplanted at Woods Hole about May 25- 
