88 THE BOTANICAL MAGAZINE. [Yoi.xxxrv.Xo.402. 



vertical diameter drawn within the circle. The solutions of the medium 

 class are shown by small dots. The three very poorest solutions (3.4) 

 are each denoted by a heavy triangle, and the remaining ones of the 

 poor class as above characterized are shown by lighter triangles, those 

 indicated by Italic type in table II having a vertical line through the 

 triangle. 



A comparison of the diagrams strongly suggests that the better 

 solutions are generally characterized by low relative partial concentra- 

 tions of the atomic group (H 2 P0 4 ) 2 , while the poorer solutions have 

 high relative partial concentrations of this atomic group. Solutions of 

 the good class are shown on the left margin of the diagram in every 

 case but one (AR1S2). Solutions of the poor class are never shown on 

 the left margin and every diagram shows one or more poor solutions 

 among the three that are nearest to the augle at the right of the. 

 diagram. 



There are, of course, a number of discrepancies among the six 

 diagrams (fig. 1), but these cannot be interpreted from the single 

 series of cultures for which we have data ; they may or may not be 

 important. But it does seem to be very strongly suggested that there 

 is no marked relation between the salts used in these incomplete solu- 

 tions and the . physiological worths of the solutions ; in other words,, 

 the Mg : Ca-ratio is not itself apparently influential in determining 

 whether a solution is good or poor. The results indicate clearly that 

 the relative partial concentration of the di-hydrogen-phosphate is the 

 controlling condition encountered here. No matter what may be the 

 proportions of nitrate and sulphate, the solutions are generally good 

 with low and poor with high phosphate concentrations. - No ratio 

 value appears as a controlling condition. 



It seems probable that this state of affairs may not be primarily 

 related to the atomic group P0 4 , but may depend upon the hydrogen- 

 ion concentration in the solution ; for the more H 2 P0 4 there is in unit 

 volume of the solution the greater should be its Ph- value. This matter 

 was not directly studied, but may readily be taken up by any in- 

 vestigator at any time, since our solutions have been described so that 

 they may be easily reproduced. The importance of hydrogen-ion con- 

 centration is receiving attention from many physiologists. When further 

 tests are to be made along this line it would be well to plan for sets 

 of salt proportions lying outside of our diagram and at its left, thus 

 including some solutions with less than one-seventh of their total salt 

 content due to the (H 2 P0 4 ) 2 -salt. These would have lower values 

 of P H , as would also the more dilute solutions already suggested 



