88 



the two week graphs that the plants of the earlier culture 

 were exposed to a lower rate of evar)oration during the last 

 two weeks of their growth than those of the two cultures start- 

 ed later in the season. It would seem that here, as in the case 

 of the cultxires at College, we are dealing with effects of 

 evaporation which arn relatively ~;reat since this condition is 

 at a critical value for the plants. 



For Easton, the dry weight remains constant from the 

 period beginning May 8 to the period beginning May E5 although 

 there is a considerable rise in temperature. This may be 

 related to the rise in the rate of evaporation during this in- 

 terval. A decrease in evaporation rate would seem to account 

 for the rise in dry weight from the period beginning May 25 to 

 the period beginning June 8. No correlation can be found be- 

 tween the low value shown by the plant graph for the period 

 beginning June 22 and the climatic conditions either as shown 

 by the four-week averages or for thalast t^fjo weeks of this 

 culture period since these were such as would be expected to 

 produce good growth. The culture beginning July 6 is low, rela- 

 tively, but this may be due to high evaporation during the last 

 two weeks of the culture period (see the period beginning 

 July 20 on the two-week graph). The dry weights of the cultures 

 beginning July 20 and Aug. 3 are also relatively lov;, for th" 

 same reason perhaps that has been given as accounting for the 

 low weight of the culture beginning July 6. Prom the period 

 beginning Aug. 17 to the end of the season, the low values of 

 dry weight shown by the plant graph may be considered as due 

 to low values of temperature and sunlight. 



