1914] SHULL—GERMINATION 67 
BECKER draws a general conclusion from his results that oxygen 
acts as a stimulus, and takes particular exception to the idea 
advanced by Crocker‘ that the oxygen increases the respiration 
and in this way initiates germination. In reviewing BECKER’Ss 
paper,’ I stated that there was no doubt that in Xanthium the 
oxygen was actually used in germination, and suggested that 
increased respiration might be identical with BECKER’s stimulus. 
While it is entirely possible that the oxygen influence is exerted 
through some other process correlated with increased respiration, 
the data presented here give the ground upon which that sugges- 
tion was based. Unfortunately, BECKER’s work gives us no data 
as to the respiration behavior of the seeds on which he worked, 
so that no comparison with the behavior of Xanthiwm seeds can be 
made at present. 
LEHMANN,’ in discussing the possibility that O, might act as a 
catalyst, accepts BECKER’s idea that oxygen acts as a chemical - 
stimulus, not merely by increasing respiration. Of course, the 
word “stimulus” is vague and indefinite. But it should not 
imply an additional absorption of oxygen, for this could not occur 
without involving oxidation of some kind, which would be respira- 
tion. Even if oxygen is conceived to be a catalyser, that concep- 
tion does not involve increased use of O,, for catalysts are not 
used in the processes they carry on. 
The biological réle of oxygen is so complex that we may not 
say its effect is always due to increasing respiration or oxidation. 
The rile, indeed, may be different in different seeds and plants. 
For instance, Arpdp PaXt’ claims that reduction of oxygen pres- 
sure even to o. 75 normal lengthens geo-presentation and geo- 
reaction time to a marked degree. This work of Padv’s still 
awaits confirmation. And although the earlier work of SticH, 
JOHANNSEN, and others indicates that this amount of reduction 
‘CROCKER, Wa., The réle of seed coats in delayed germination. Bor. Gaz. 
42:265-291. 1906, mE 
§ Bor. Gaz. 54:433. 1912. 
* LEHMANN, E., und OrrenwAtper, A., Uber katalytische Wirkung des Lichtes 
bei der Keimung lichtempfindlicher — -_— Bot.*5: 337-3%- inal 
7 Pat, Arpho, Analyse des a ee ung. 
Jahrb. Wiss. Bot. so: 1-20, 1grt. deck 
