212 Variations in Growth-Rates [410 



period. At the end of each week several different kinds of 

 measurements of the plants were made, and the data thus 

 obtained were studied to bring out the seasonal variations in 

 growth-rates. Since the solutions were alike for all sets and 

 the seedlings used were selected for likeness, it is fair to sup- 

 pose that observed differences in growth-rates, between the 

 different sets of cultures, must have been mainly due to fluc- 

 tuations in the uncontrolled conditions of the surroundings, 

 such as temperature, light and the evaporating power of the 

 air. 



The experiments were carried out in one of the experiment 

 greenhouses of the Laboratory of Plant Physiology. Xo 

 artificial shade was applied to the greenhouse. Two sets of 

 cultures were always carried out simultaneously, one under 

 unmodified greenhouse conditions and the other in a cheese- 

 cloth chamber in the greenhouse, but the data obtained from 

 the chamber cultures will not be dealt with in the present 

 paper. A continuously rotating table 76 cm. in diameter was 

 used in each case, the jars standing near the margin of the 

 table. 



Japanese buckwheat, Fagopyrum esculentum Moench., was 

 employed, and Shive's * three-salt nutrient solution, no. 

 R 4C2 (total osmotic value 1.75 atmospheres), was used 

 throughout the entire series. Aside from renewing the 

 solution at the middle of the four-week period, water was 

 always added at the end of the third week of growth, to bring 

 the solution back to its original volume. When the transpi- 

 ration rates were excessive a still further addition of water 

 was made during the fourth week of growth, in order to pre- 

 vent the root systems from becoming unduly exposed. The 

 first experiment began Feb. 14, 1916. 



Of the plant characteristics measured at the end of each 

 four-week period of growth, only stem height, total dry weight 

 and total area of the leaves (one surface only) are here con- 



1 Shive, John W., "A study of physiological balance in nutrient 

 media." Physiol. Res. I: 327-397. 1915. 



