io BOTANICAL GAZETTE [july 



equilibrium. The tests were confined finally to the region of soil 

 moisture from air-dry to the wilting coefficient, for with a higher 

 moisture content the seeds always became saturated with water. 

 In the case of this sand it was not until the water content was 

 reduced to about i per cent that a noticeable "back pull" was 

 developed by the soil. 



This method is obviously open to the criticism that friction 

 retards the movement of water in dry soils, and that the seeds 

 therefore do not reach actual equilibrium with the total soil mass, 

 but only with the soil lying very near them. In order to meet this 

 difficulty a rotation method was adopted which brings the seeds 

 constantly into contact with fresh soil particles. 



A definite amount of dry soil, usually 60 gm., was taken, and 

 the desired amount of water thoroughly mixed with it. In this 

 condition the soil was divided finely enough to pass through a 

 2 mm. sieve. The moist soil was then placed with dry seeds in 

 a wide-mouthed 200 cc. bottle, without completely filling it, so 

 that rotation would constantly mix the soils and seeds. The bot- 

 tles were carefully sealed with heavily shellacked corks to prevent 

 loss of water during the period of rotation. 



These bottles were arranged on rotating wheels, driven by a 

 motor and controlled by a speed reducer (fig. 1). The range from 

 air-dry to wilting coefficient was divided into 10 fairly equal 

 divisions, giving n tests in each series. The rotation was con- 

 tinued for 15 days, this time having been chosen after making 

 tests as to the effect of differences in duration of the experiment 

 on the amount of intake by the seeds. For instance, no. 2/0 sand 

 with about 0.2 per cent moisture added permitted an intake of 

 22 per cent of their weight by the seeds in 5 days, and a parallel 

 test showed 21.7 per cent intake in 10 days. Fifteen days, there- 

 fore, seems ample time for the establishment of equilibrium. At 

 the end of the time the bottles were opened, and the seeds very 

 rapidly separated from the soil and brushed free of all dust with a 

 camel's-hair brush. The soil and seeds were both placed in weigh- 

 ing bottles as quickly as possible, to prevent serious loss of water 

 by evaporation. The soil was weighed carefully and dried at 

 104 C. until loss ceased. The seeds also were weighed. The 



