Oct. IS, 1919 Relation of Nutrient Medium to Plant Absorption 75 



of absorption, as will be made evident later, involves the whole technic 

 of solution-culture experimentation in its relation to the size of culture 

 vessels and frequency of renewal of solutions, while the interpretation of 

 the data likewise must take into consideration the nature and extent of 

 absorption. 



In all of the present experiments a selected Beldi variety of barley was 

 used as the test plant. Although the conclusions of this article are based 

 on experiments with barley, it is our opinion that the general principles 

 of nutrition and absorption deduced apply as well to at least most of the 

 common plants of agricultural interest. Germination was accomplished 

 very conveniently by Waynick's (52) method. The bottles for the solu- 

 tion cultures were coated on the outside with black paint and then 

 wrapped with white glazed paper. The latter precaution is very neces- 

 sary when the cultures are exposed to strong sunlight, on account of heat 

 absorption. Wedges, slightly truncated, were cut from the cork stoppers, 

 and the seedlings were fixed in the openings by means of cotton. As the 

 plants grew and tillered, the size of the openings was increased from time 

 to time by cutting off further segments from the wedge. This part of 

 the technic is important, since there should be no mechanical restric- 

 tion to the development of the plant. In fact it may be stated as a gen- 

 eral principle that the technic employed should place no limitation on 

 the growth of the plant other than that caused by the variables under 

 consideration. 



Two sizes of bottles were used, of approximately 1,000- and 2,200-cc. 

 capacity. In some experiments only one plant was placed in each bottle, 

 in others two plants. Thus a relatively large volume of solution per plant 

 was provided. The more detailed discussion of this point is reserved 

 until later in the article. The volume of solution was maintained as 

 constant as possible by the addition of distilled water daily or sometimes 

 oftener. 



In order to support the growing plants, glass rods were fixed in the corks 

 and provided with loose loops made of cotton string. Great care was 

 taken that there should be no crowding together of the leaves, for it is 

 essential that each leaf receive the maximum light, and this would be 

 impossible if the plants were bound tightly to the supporting rod. Most 

 of the corks were dipped in melted paraffin previous to use. Any excess 

 of paraffin is, however, to be avoided, since it may soften in the sunlight 

 and injure the seedling at the point of contact. 



In making up the nutrient solution the ordinary supply of distilled 

 water was used. This had been in contact only with glass or block tin. 

 At no time was there any evidence of toxicity due to the distilled water. 

 Comparative tests, using water treated with "G Elf" carbon black as 

 recommended by the Bureau of Soils, did not indicate any advantage in 

 this treatment. Baker's analyzed chemicals were usually employed in 

 making the nutrient solutions. Strong stock solutions of calcium nitrate 



