390 BOTANICAL GAZETTE [NOVEMBER 
Moreover, there is a strong correlation between the growth of the hypo- 
cotyl and cotyledons. Normally the former grows first, and the latter do 
not enlarge until the root is well established. But if the seeds with coats 
on are placed in an atmosphere composed largely of oxygen, this normal 
correlation is reversed, the cotyledons elongating before the hypocotyl begins 
to develop. The testa is comparatively thick over the hypocotyl, very thin 
over the cotyledons, and certainly admits oxygen more quickly to the cotyle- 
dons than to the hypocotyl. The cotyledons are less sensitive than the 
other parts of the embryo, and require more oxygen to activate them than 
would be necessary for the hypocotyl. It is perfectly clear, then, that much 
of the oxygen used by seeds which germinate with the seed coats intact and 
in high oxgyen pressure is due to consumption of oxygen by the seed coats 
and the cotyledons, very little being used by the hypocotyls. In my 
experiments the pressure has been determined for the very sensitive hypo- 
cotyl, which always grows first if the coat is off, and the pressure required is 
low. I believe that these two points fully explain the difference in oxygen 
pressure necessary to germination with coats off and coats intact. 
urther work is necessary to determine the exact relation of temperature 
to the oxygen pressures required, and series at high temperatures will be 
compared with series at low temperatures to obtain definite data on this 
point. 
Fresh seeds will be collected this fall and tested immediately after they 
have ripened, to determine whether there is any after-ripening, whether 
the oxygen pressure necessary for germination is greater or smaller before 
the period of drying, freezing, and resting than it is later. 
Acknowledgments are due to Dr. Witt1am Crocker, under whose 
direction the work here recorded was done.—Cuas. A. SHULL, Transylvania 
University, Lexington, Ky. 
