4i8 



BOTANICAL GAZETTE 



[DECEMBER 



Relative transpiration rates 



Thus far we have considered largely transpiration losses of 

 different individuals of the batteries of the various species, with 

 only occasional reference to comparative losses of different species. 

 It may be well, therefore, to present data showing the actual losses 

 of different species based upon unit area. These data have been 

 summarized in table IX. While the dates between readings are 

 not synchronous in all cases, they are at least nearly so, and fig. 15, 



TABLE IX 



Comparative transpiration losses from unit areas of surface of broad- 

 • leaved and evergreen trees 



which gives the temperature and humidity, together with the 

 record from the atmometers, shows that the overlapping periods 

 are quite uniform. 



Relative midsummer transpiration rates of broad-leaved trees 



and conifers 



During the following summer, while the writers were carrying 

 on other investigations in the Rocky Mountains of the Pike's Peak 

 region of Colorado, opportunity was afforded to compare the 

 summer transpiration rates of different tree species. 



Seedlings of white elm and soft maple grown from seed at the 

 Alpine Laboratory near Manitou, Colorado, and at an altitude of 

 8000 ft., together with mountain maple (Acer glabrum Torr.) 

 obtained from the forest, were the broad-leaved species used. 

 Yellow pine, Douglas fir, and Engelmann spruce were the conifers 

 employed. The pines were secured from the Fremont Experiment 

 Station; while the other trees, like the mountain maples, were 



