9;^ 



the corresponding exposed cultures for the perbds beginning 

 June 18, July 2, and July 15 and the stem height is greater 

 for the covered station than for the exposed station for the 

 periods beginning June 4, July E and July 15. The highest 

 value of leaf-product occurs in the period beginning July 15 

 for the covered and in the period beginning July 16 for the 

 exposed two- week plants. Both sets of cultures show two 

 maxima, in the plant graphs but these are much higher in the 

 case of the covered plants than in the case of the exposed. 

 In the four- week graphs of the covered plants, leaf area is 

 higher than dry weight for the whole season, while in the expos- 

 ed plants, the granh of leaf ar'?a is well below the grai^h of 

 dry weight from the period beginning May 23 to the period be- 

 ginning July 16 inclusive. The maximum for all the growth 

 measurements of the four-week exposed plants occurs in the 

 pertod beginning June 19 while in thej-^overel set of cultures 

 the maximum occurs in the period beginning July 2. Also, the 

 graphs of the four-week plants all exhibit higher values than 

 the graphs of the two-week plants for most of the culture per- 

 iods of the season. This is especially true of the leaf-area. 

 The effect of covering the plants with glass would seem to be 

 to produce a relatively high rate of leaf expansion, and this 

 in spite of the fact that evaporation is somewhat higher for the 

 covered than for the exposed plants. 



The two-week plant data for the covered station at 

 Baltimore are plotted to a scale one-half as great as the scale 

 used in plotting the exposed plant values on account of the 

 high values of height and leaf-product shown by the covered 

 culture beginning July 9. The values of both leaf-product and 



