36 THE UNIVERSITY SCIENCE BULLETIN. 



But Shull (9) also found that air-dry seeds of the cocklebur 

 (hygroscopic moisture, 7 per cent) had an internal attractive 

 force for water of 965 atmospheres, or over 14,000 pounds per 

 square inch, and that when these seeds had absorbed an addi- 

 tional 7 per cent of water this force had dropped to less than 

 400 atmospheres. The absorptive power shown by the three 

 instances referred to in the paragraph above seems to bear out 

 his landings. In the case of the other six, there was evidently 

 sufficient water in the sand to allow an equilibrium to be 

 reached between the opposing external and internal forces be- 

 fore the percentage of water present was pulled to the low 

 figure reached by the other set. 



Another way of looking at the results mentioned above, num- 

 bers 39, 41, and 43 were given about the same amount of 

 water each, practically half that required for the wilting coeffi- 

 cient of this sand, and the results are practically the same. 

 By calculation, disregarding that removed in sampling, each 

 tumbler contained a total water content of about 1.3 grams. 

 Of this, the seeds absorbed about half, 0.48, 0.62, and 0.72 

 grams, respectively. According to table 1, 41 per cent of the 

 weight of the corn seed is the minimum for fair germination 

 when conditions are favorable. Forty-one per cent here is 0.73 

 gram. The maximum used as shown in the table is 55 per cent, 

 or, that would be here, 1 gram. With 0.48 to 0.72 gram of 

 water used here, with 0.73 to 1 gram used when conditions 

 are favorable for absorption, with the weight of the seeds 

 practically the same, and with the moisture content of the soil 

 pulled down to 0.29-0.41 per cent, it would seem that when the 

 lower limit of possible water absorption from the surrounding 

 soil was reached by these seeds in the cases quoted, they had 

 been unable to secure water enough for germination. The 

 lower limit is probably somewhere about 0.75 to 0.85 per cent. 



In comparison, number 36 used but about 0.64 gram of water 

 for complete germination, and when this was complete, as 

 much water remained in the sand as each of the three men- 

 tioned had to start with. But why should number 36 germin- 

 ate when it had absorbed 0.64 gram of water and number 43 

 fail to do so when it absorbed 0.72 gram? Has the rate of 

 absorption or the amount remaining in the soil anything to do 

 with it? 



