1919] 



CRIBBS—TILIA A .1/ ERICA X. 1 



277 



Fig. 1 1 is a composite graph in which the curve for each station, 

 is plotted from the average of all the readings taken. This figure 

 shows the relative transpiring power of Tilia in the different dune 

 environments, and it will be seen that there is a very pronounced 

 increase in the index of transpiration when considering the sta- 

 tions in their order from the mesophytic to the more xerophytic 

 habitats. 



Fig. 11. — Composite graph of all transpiration readings taken at stations A, B, 

 C, D, and E, showing increase in transpiring power accompanying increased exposure 

 of habitat. 



These curves being averages, and hence not recording daily 

 variations, do not give to best advantage the typical daily curve. 

 The occurrence of the maximum about 12:00 noon in the more 

 mesophytic situations, however, and an earlier occurrence from 

 9:00 to n :oo a.m. on the open sands, is noticeable even in the aver- 

 age graphs, as is also the earlier morning rise characteristic of the 

 exposed stations. 



Fig. 12 includes averages of all the different factors taken in 

 connection with the dune transpiration studies. The unit spaces 

 at the top of the graph have the following values: evaporation 



