71) 



light intensity and a considerable decrease in evaporation 

 rate, with the plant graph rising sharply, '^he graph of dry 



weight then descends from the period beginning June 19 to 

 the period beginning July 3 and ^'^ightly^^rises, from the period 

 beginning July 3 to the period beginning July 16. Neither 

 of these 7;ould be expected from the values of the four-week 

 averages. If , now, the dry weight graph from the period begin- 

 ning May 23 to the period beginniiig July 16 be compared 'vith 

 the two-week evaporation graph from the period beginning 

 Jime 5 to the period beginning July 31 it will be seen that 

 the dry weight exhibits a very consistent inverse relation to 

 the evaporation as shown by the opposite slope of the two 

 graphs from period to eriod. The dry weight at this station 

 sesms thus to be determined during the first five four-week 

 periods largely by the evaporation during the last two weeks of 

 each period. From the period beginning July 16 tc the end of 

 the season the graph of dry weight descends following & corres- 

 ponding downward slope in the graphs of sunshine and temperature 

 indices shown by the four-week averages of these conditions. 

 Evaporation during these -ericds is low and seems not to affect 

 the plants. The sharp downward slope of the dry weight graph 

 from the period beginning Aug. 14 to the period beginning 

 Aug. 2? is probabljr accounted for by the lact that the tem- 

 perature value is very low during the last two weeks of the 

 latter period. ?or this station sunshine and temperature in- 

 dex values show oniy relatively small fluctuations throughout 

 the season and the plants exhibit rather clearly the effect of 

 evaporation. 



■'^'or Chewsville, the values of dry weight for the first 



