WATKK SOILS. 651 



supplied less water to seeds and plants than the more fertile soils, and there was no 

 observable difference in the amount of moisture absorbed by seeds in soils of the 

 same water content whether manure bad previously been added to the soil or not. 



" The fact that the availability of the moisture and its dissolved salts is due to 

 something other than the texture or physical condition of the soil was shown In- 

 growing plants in an aqueous extract of the soil, when it was found that the plants 

 showed the main characteristics of growth and development that were associated 

 with them when grown in the soils themselves." 



The following simple method of studying transpiration was used: " Seedling plants 

 were grown in prepared solutions contained in 2-oz. bottles, each with a stopper having 

 slits in the circumference, into which the plants were fitted, with some cork slips 

 over them to hold them in place and to prevent direct evaporation from the inside of 

 the bottle. The bottle was of black opaque glass, anil the plants were kept in the sun 

 throughout the day. The bottles containing the plants were weighed daily, and the 

 loss of weight taken as the measure of transpiration. Such precautions were taken 

 that the amount evaporated directly from the bottle was so small that it could he 

 ignored, while the daily amount transpired by the plants was from two to ten times the 

 weight i >f the plant, and the increased growth of the plant from day to day during the 

 period of the experiment is therefore taken as negligible for purposes of the experi- 

 ments." 



The experiments with soil extracts, culture solutions of various kinds, as well as 

 with soils, were made in glass tumblers or wire baskets :! in. deep and 3 in. in diame- 

 ter, coated with paraffin. The experiments were made with wheat seed lings, but no 

 attempt was made to carry the plants to maturity — 5 or 6 weeks being the extreme 

 limit of growth in the experiments reported. The results of a large number of 

 experiments with different culture solutions and soils of different kinds are reported 

 in detail, but few conclusions are drawn from the data. 



In the culture experiments it was found in general "that a concentration of about 

 170 parts per million of total dissolved salts was the most desirable, provided that at 

 least 1 part per million of each constituent was present." 



The centrifugal method of mechanical soil analysis, L. J. Briggs, F. 0. 

 Martin, and J. R. Pearce ( U. S. Dept. Agr., Bureau of Soils Bui. .'!, ///>. 38, pis. ..', 

 till*. ?).— This bulletin, which is intended to take the place of earlier publications on 

 the subject, contains a description of the centrifugal method of mechanical soil anal- 

 ysis as used in the Bureau of Soils, together with the results of an investigation of 

 the possible sources of error. The procedure followed by the Bureau in collecting 

 and preparing the samples for analysis is stated, and a brief description is given of 

 other methods of mechanical analysis, several of which have been extensively used 

 in the United States. The chromic-acid method employed by the Bureau for deter- 

 mining organic matter is also described. 



The apparatus and methods used are described in detail, from the sifting of the 

 soil through a 2 mm. sieve and its disintegration by a mechanical shaker, through 

 the various stages of the separation of the different grades of particles by means of 

 the centrifugal machine and by sedimentation. 



Experiments with the Brown sampling machine (described in Office of Experi- 

 ment Stations Circ. 34, revised) showed that "a mechanical sampler is superior to the 

 spatula for subsampling soils in which [the two coarsest] groups are present in any 

 quantity. This applies also to samples in which aggregates exist larger than 0.5 mm. 

 The mechanical sampler has the disadvantage of not giving samples of uniform 

 weight" and "some inconvenience in calculation is thereby introduced." 



While the results obtained in a study of the effect of oven-drying were not conclu- 

 sive, they "indicate that drying a soil at 110° C. does not seriously modify its 

 mechanical composition, as determined in the moist state." It was found "that 



20085— No. 7—05 3 



