BOOKS AND CURRENT LITERATURE 147 



results agreed with the calculated osmotic values, as nearly as could be 

 measured by the cryoscopic method. The increase in yield in the best 

 solution of Tottingham's supra-optimal series was 53% and 47%, for 

 tops and roots, respectivelj^, over the yield from Knop's solution of 

 this concentration. 



In the solutions giving the highest dry weight of tops the Mg/Ca 

 ratio was 1 : 1 for the optimal, 2:1 for the suboptimal, and 3.3 : 1 

 for the supra-optimal concentration, while in Knop's solution this ratio 

 is 1 : 3. An apparently characteristic form of leaf injury was observed 

 with the highest values of this ratio in the optimal and supra-optimal 

 series. A decrease in transpiring power attended severe injury of this 

 kind. Also, in the supra-optimal series another form of leaf injury 

 accompanied the lowest values of the Mg/Ca ratio. 



Tottingham's discussion brings out the fact that the effect of a mix- 

 ture of salts in solution upon the amount of dry matter produced and 

 upon the development of the plant in general, depends upon the com- 

 plex balance of all of the salts in the solution, and not simply upon the 

 ratio of one substance to another; and also that the effect of a given set 

 of the proportions of the nutrient salts varies with the total concentra- 

 tion of the nutrient solution. 



If any feature of the experimentation here reviewed is to be adversely 

 criticized it is perhaps the employment of distilled water as a control 

 medium; since plants growing in distilled water soon become unhealthy, 

 this cannot be considered a perfect control. A more satisfactory con- 

 trol medium should give healthy plants that continue to grow and 

 respond to external conditions throughout the period of a given experi- 

 ment. This and other points in the technique employed will of course 

 become more refined as more work of this kind is done. On the whole 

 this investigation appears to be the most thorough study of its kind 

 that has yet appeared, and perhaps its most valuable feature is the 

 method developed for studying the comparative effects of complex salt 

 solutions in a logically complete way. — Sam F. Trelease. 



Temperature and the Rate of Growth. — Leitch has recently 

 completed a study of growth in pea roots, as affected by temperature, 

 in the laboratory for plant physiology of the University of Copenhagen. 

 It was found that the relation of growth to temperature between 2°C.' 

 and 29°C, is to.be expressed by a curve similar to that of respiration 



^Leitch, I., Some experiments on the influence of temperature on the rate 

 of growth in Pisum sativum. Anrl. Bot. 30: 25-46, January, 1916. 



