112 
WM. CROCKER 
in seeds of the type now under discussion may determine their 
abihty to germinate in Hmited oxygen supply and that agencies like 
light and salts act indirectly through sugar formation or carbohydrate 
hydrolysis. This and other possibilities need careful experimental 
study in this connection. 
Matters are made more difficult here by the fact that we do not 
know the exact method by which oxygen acts in determining growth 
and growth rate of organs of seed plants. Nabokich^^ gives it a 
multiple role. Directly, it stimulates growth as do salts and other 
substances. This function can be cared for by various other reagents. 
Next, it oxidizes what would otherwise be fatal products of anaerobic 
respiration and thereby makes continued life possible. Finally, he 
probably would not deny that indirectly at least it is important in 
releasing necessary energy for growth through normal respiration. 
In connection with germination Becker^^ speaks of oxygen as having 
a catalytic function and Lehmann^i connects it with the hydrolysis of 
proteins, thus furnishing substances necessary for the growth of the 
embryo. The assumptions of these authors are 'in great need of 
experimental evidence; they have such difficulties to meet as the 
facts that there is greatly increased oxygen consumption under in- 
creased oxygen pressure and that hydrolysis of proteins is extensive 
in certain seeds in oxygen-free^^ germinators. Kidd^ finds that the 
narcotic concentration of carbon dioxide decreases with decreased 
oxygen pressure and believes that oxygen supply in seeds of the type 
under discussion operates indirectly through the anaesthetic action 
of carbon dioxide. Shull^^ |g inclined to think that in the cocklebur the 
effect of oxygen is through increased respiration, for here the oxygen 
consumption increases greatly with increased partial pressure and with 
coat removal. 
The unsolved problems here are among the most difficult and funda- 
mental of those met in growth.^"^ 
Dude^^ finds that imbibed seeds in vacuo are soon killed by accumu- 
lation of toxic materials of intramolecular respiration. Of the five 
species studied the life duration in this condition ranged from about 
3° Nabokich. Beih. Bot. Centralbl. 26: 7. 1910. 
2^ Lehmann. Biochem. Zeitschr. 50: 388. 1913. 
^2 Godlewski. Bull. Acad. Sci. Cracovie. 9: 705. 1912. 
33Shull. Bot. Gaz. 57: 64. 1914. 
3^ Hober. Phys. Chem. Zelle. u. Gewebe. 752-780. Berlin, 1914. 
35 Dude. Flora 92: 203. 1903. 
