360 
GENETICS: B. M. DAVIS 
other two provinces. The normal marine junction of the Cataract 
and Brassfield seas is prevented by the Medina delta of sands. For 
these reasons, Medina, Cataract, and Brassfield are to be retained as 
names for independent marine faunas and formations. The details 
leading to these conclusions are set forth in a contribution entitled 
'Medina and Cataract formations of the Siluric of New York and On- 
tario,' Bulletin of the Geological Society of America. 
A METHOD OF OBTAINING COMPLETE GERMINATION OF 
SEEDS IN OENOTHERA AND OF RECORDING THE RESI- 
DUE OF STERILE SEED-LIKE STRUCTURES 
By Bradley Moore Davis 
DEPARTMENT OF BOTANY. UNIVERSITY OF PENNSYLVANIA 
Presented to the Academy, May 4, 1915 
All genetical workers with Oenothera shortly become aware that 
generally only a small proportion of the seed-Hke structures sown in 
their seed pans produce seedlings before the pans are emptied to give 
place in the hot house for the developing culture. My own practice 
has been to keep seed pans from eight to ten weeks only, as it is uncer- 
tain, if sowings are made in January, whether seedUngs appearing later 
can be brought to maturity during the summer. For the past three 
seasons I have counted the seeds sown and thus have obtained some 
information on the relative degrees of fertility in my cultures which in 
some cases have been surprisingly low. But this procedure does not 
give accurate data on the proportion of fertile seeds to sterile seed-like 
structures for the reason that germination of Oenothera seeds in earth 
is very irregular and may be delayed far beyond the time that it is con- 
venient or possible to keep the seed pans. Seeds sown in earth are 
obviously lost for further enquiry as to the fact of theirviability, a propor- 
tion of seedlings appears but, as for the residue, that cannot be examined. 
The technical problem of obtaining from sowings of seeds cultures 
that will accurately represent the genetical possibilities of the sowing 
is under these conditions difficult. In Oenothera work this problem is 
vital for exact studies since through the delayed germination may be 
lost not only peculiar individuals but possibly, in the case of hybrids, 
entire classes of segregates. It is probably safe to say that no culture 
of Oenothera has as yet been described in which we may feel confident 
that all of the viable seeds have germinated. Consequently we cannot 
be certain that any of the reported percentages of 'mutants' or ratios 
of segregates from hybrids are correct. Furthermore it is important 
