October 13, 1922] 



SCIENCE 



421 



The text-ibook under review will doubtless 

 remain a standard for many years. It may be 

 too extensive to meet the wants of most insti- 

 tutions for a first course but it will probably 

 be consulted by many teachers who prefer to 

 place briefer treatments in the hands of their 

 students. The high mathematical attainments 

 of its authors are naturally reflected in many 

 details of treatment, and inspire deserved con- 

 fidence in the accuracy of the statements re- 

 lating to matters of fundamental importance. 

 The modern tendency towards the insertion of 

 numerous historical notes in elementary text- 

 books on mathematics is not followed here. 



It may be added that the authors state in a 

 foot-note on page 177 that a tangent can not 

 be defined as a line meeting the conic in a 

 single point. The opposite view was recently 

 expressed by Professor Cajori in an article 

 published in School Science and Mathematics, 

 volume 22, page 463, where the author tries to 

 support an inaccurate statement found on page 

 163 of the second edition of his "History of 

 Mathematics," 1919. It is here stated that 

 Roberval "broke off from the ancient definition 

 of a tangent as a straight line having only one 

 point in common with a curve." It may also 

 be noted here that some readers might question 

 whether it should be said that a mathematical 

 argument can be convincing without being con- 

 clusive, as is implied by the authors in a foot- 

 note appearing on page 180. In view of the 

 extensive literature on Greek algebra the sec- 

 ond paragraph of the Introduction is mis- 

 leading. 



G. A. Miller 



University of Illinois 



SPECIAL ARTICLES 

 WATER CULTURE EXPERIMENTATION 



As a one-salt solution is the simplest possi- 

 ble salt solution, so the simplest growth media 

 that can be devised for plants, provided they 

 need but two elements at a time, should be the 

 proper combination of one-salt solutions. Be- 

 cause green plants require at least seven salt 

 elements, available to and absorbed through the 

 roots, complete nutrient solutions having tliese 

 elements present together are employed as the 

 media in which the plants are grown. The use 



of at least three simple salts plus a trace of 

 iron (added as a salt) is required to supply the 

 growth media with the necessary elements. 



The writer has recently grown wheat for a 

 period of three months, which included the 

 heading out stage of the plants, in a combina- 

 tion of single salt solutions of KNO3, CaSO^ 

 and MgHPO^ (each of .01 mol. concentration). 

 The plants grown in these solutions were equal 

 or comparable in their various features of 

 growth, including that of total dry weight, to 

 those of plants grown contemporaneously in 

 complete well-balanced nutrient solutions pre- 

 pared either with the above named salts or 

 with other salts supplying the same elements. 



The salts named appear to be the only three 

 salts that can be used as a combination of three 

 single salt solutions that permit of normal and 

 undiminished growth of wheat. This is the 

 conclusion arrived at from an investigation of 

 culture tests using those salts singly as com- 

 binations of one-salt solutions that were out- 

 lined as combinations of three-salt solutions 

 (complete nutrient solutions) in the Plan of 

 Cooperative Eesearch on the Salt Requirements 

 of some Agricultural Plants.^ 



Because the mono-basic phosphates given in 

 the plan were found to be too acid for these 

 tests with single salt solution, the diabasic 

 phosphates of calcium and magnesium were 

 substituted for those of the respective mono- 

 basic phosphates. It appears, therefore, that 

 by using the proper salts, wheat plants grow 

 as well with only two nutriment elements 

 present in the media at one time (exclusive of 

 a trace of iron supplied at weekly intervals to 

 all cultures) as they do in complete nutrient 

 solutions. 



The set of plants that made best growth, of 

 those sets tested, as combinations of one-salt 

 solutions named, were apportioned among the 

 solutions as follows : four days continuously in 

 KNO3, one day in CaSO^ and one day in 



1 See Plan of Cooperative Eesearch on the Salt 

 Eequirements of Eepresentative Agricultural 

 Plants, prepared for a Special Committee of the 

 Division of Biology and Agriculture of the Na- 

 tional Eesearch Council. B. E. Livingston, editor. 

 Baltimore, 1919. 



