158 T. G. YUNCKER 



It will be noted in Table I that in the first experiment the water 

 requirement is somewhat higher than for the later experiment. 

 This can be accounted for by the fact that the plants in the first 

 experiment were younger and growing much faster than those in 

 the later. The figures in both cases show a constant relation- 

 ship between the series. The rate of transpiration in GM^H^ 

 shows the same relation to moisture content as does the water 

 requirement, as one would naturally expect, for the more water 

 lost in GM^H would indicate the greater amount the plant would 

 use in the production of a given amount of organic material. 

 The rate of transpiration in GM^H for the day and night series 

 shows a greater amount per unit area, but this is undoubtedly due 

 to the fact that this series was run at a time when there was 

 a greater amount of sunshine and conditions for transpiration 

 were better than for the other series. 



PHOTOSYNTHESIS EXPERIMENTS 



The object of these experiments was to determine the rela- 

 tion between the weights per unit area of leaf surface at different 

 periods of the day and the three percentages of soil saturation. 

 To obtain these data it was essential to obtain leaf clippings at 

 regular intervals. Six-hour intervals was considered as being 

 sufficiently frequent. The plants were placed in a convenient 

 position on the greenhouse bench and, starting at 6.00 p.m. 

 clippings were made every six hours until the following day at 

 6.00 p.m., making five clippings in all that were taken for each 

 experiment. In taking the clippings two leaves were removed 

 from each potometer of four plants. At each succeeding period 

 the clippings were taken as nearly similar to the preceding ones 

 as it was possible to do. After each set of clippings was made 

 they were taken immediately to the laboratory where tracings 

 were made of them from which the size was obtained. The 

 leaves were steamed thoroughly, dried and from the area of the 

 leaves, the amount of leaf substance, by weight, per given unit 

 of area was obtained. 



1 The expression GM-H indicates the reduction of the transpiration data to 

 grams of loss per square meter per hour. 



