June, 1920.] SOME SOLUTION CULTURES OF WHEAT 85 



*in table II by black-face type. None of these has any score value of 1 

 by any criterion. Those shown by Italic type all have the score value 

 2 by some criterion and thus may approach the medium class. All 19 

 solutions of the poor class are surely of very low physiological worth. 



It appears that the most obvious outcome of this experiment is 

 the fact that some of these solutions without any potassium did give 

 very good growth of the plantlets and that the best of these are to be 

 considered as ten-fourteenths (or five-sevenths) as good as the control 

 solution, which is one of the very best solutions for young wheat 

 plants thus far described. This ratio, ten-fourteenths, is of course the 

 ratio of the physiological worth of the three best incomplete solutions 

 (1.4) to that of the control solution (1.0). As has been said, the 

 physiological worths of the solutions are to be considered as pro- 

 portional to the reciprocals of their generalized score values. The 

 generalized score value for the best solutions without potassium is 

 1.4, and that for the controls is 1.0, so that we have the expression 



-y-j — = — j~rr to represent the ratio of their physiological worths, the 



valuation of this expression being , 1 . , -=-, or 0.714. 



To give the reader a mental picture of what has been regarded as 

 good growth in the preceding discussion, we may take' advantage of 

 the fact that the score values for the criterion of height (H) were 

 originally derived from actual measurements, recorded in centimeters. 

 The tallest plants of the entire series were in a control culture and 

 this culture showed an average height of 44.5 cm. The average height 

 of all the control plants was 40.8 cm. and the average height for the 

 three best cultures without potassium (AR2S1, ER3S1 and ER4S1) 

 was 39.9 cm. By the criterion of height alone these three best in- 

 complete solutions are almost as good (39.9-^40.8 = 0.98) as the 

 controls. Of course the score values obtained for these three solutions 

 by means of the other plant criteria that were used, also take part in 

 the generalized value (1.4), which, as has been said, is only five- 

 sevenths as large as that for the control solution (1.0). 



Many nutrient solutions have been put forward in the literature 

 as suitable for green plants. Thirteen of these were simultaneously 

 compared by Shive (1916), using young wheat plants. Shive's table 

 XIV shows the comparative values that he obtained, ranging from 

 1.00 (Sachs' and Schimper's solutions) to 1.74 (Shive's R5C2— 1.75 

 atm.). Every one of these solutions contains all of the chemical 

 elements generally regarded as essential in the medium for ordinary 



