iq 1 4 ] CROCKER &> DAVIS— DELAYED GERMINATION 311 



independently of oxygen supply. It is evident, therefore, that 

 lack of oxygen cannot be the cause of dormancy in these seeds. 

 Maze (20) finds that seeds of most land plants will not germinate 

 under water, and that storage under water in otherwise good 

 germinative condition soon leads to loss of vitality. Good aera- 

 tion of the water or addition of hydrogen peroxide to it will lead to 

 germination under water. In contrast to this, Guppy (15) , Fischer 

 (12), and others have shown that seeds of many water plants may 

 lie in water for years without germinating and still retain their 

 vitality. This in itself suggests that the seeds of water plants 

 are very different from land plants in their behavior toward a 

 deficiency in oxygen. In Alisma we have shown that the embryo 

 in the intact imbibed seed lacks much of being fully saturated with 

 water. This probably holds for the seeds of many water plants, 

 as one of us (6) has pointed out, and may in part account for the 

 lack of injury from long storage under water. So far as investi- 

 gated, seeds of water plants have extremely low minimum oxygen 

 pressures for germination, if indeed any free oxygen is necessary 

 for the process. The fact that their physiological processes can 

 go on normally under water probably accounts in part for the capa- 

 city for water storage. One of the authors (6) has already pointed 

 out this fact for seeds of several water plants. 



During this investigation we have made a large number of 

 experiments determining the relation of the amount of oxygen 

 pressure to the growth rate, course of development, and chlorophyll 

 formation in Alisma seeds and seedlings. We need mention only 

 a few of the data and general results. 



In all the experiments with the effect of various oxygen pressures 

 on germination and development, the embryos used were partially 

 freed from the coats and in an uninjured condition. Part of the 

 experiments were run in vacuo and part by the displacement of 

 air by hydrogen. In general, the cultures in hydrogen did not do 

 as well as those in vacuo. This may be due to a slight toxicity of 

 hydrogen itself or to some impurity in it. The hydrogen was 

 derived from the electrolytic dissociation of water and freed from 

 oxygen by passing it through a quartz tube filled with small copper 

 disks and heated white hot with a blast flame. The hydrogen 



