76 CARNEGIE INSTITUTION OF WASHINGTON. 



formity among the relative transpiration maxima for the rain-forest 

 and for the desert than might be expected. When such a uniformity- 

 is considered in the Hght of the fact that the evaporation is very- 

 many times greater in the Arizona desert than in the Jamaican rain- 

 forest, it forces the conclusion that the transpiration-rates in the 

 plants of the two regions must be roughly proportional to the 

 evaporation-rates, else the relative transpiration-rates would not 

 remain so nearly equal. In short, it is the desert plants in which the 

 rate of transpiration is high and the rain-forest plants in which it is 

 low, which is quite the reverse of the commonly accepted view. 



Altitudinal Gradients of Growth-rate, hy Forrest Shreve. 



Field-work on the relation of altitudinal differences of climate to 

 the growth-rate of the yellow pine has been continued in the Santa 

 Catalina Mountains and has also been prosecuted in the vicinity of 

 the San Francisco Peaks in northern Arizona. In the latter region 

 the pine occurs through a vertical range of 4,000 feet, closely corre- 

 sponding to its distribution in the Santa Catalina Mountains, and 

 extended stands of it may there be found on deeper soils than those 

 of the abrupt slopes of the Santa Catalinas. 



The work as carried out has had in view the securing of altitudinal 

 gradients of growth-rate and also the determining of the influence 

 upon the rate of growth which is exerted by soil character, density of 

 stand, age of tree, and form of crown. It has been found necessary 

 to select areas for study on unlike soils at the same altitude, and to 

 use trees of all ages and of all forms of crown, in stands of differ- 

 ing density, in order that these factors may not mask the effect of 

 the climatic diversity at the different altitudes. The growth data 

 secured in the immediate vicinity of Flagstaff, Arizona, afford an 

 opportunity for comparison of the annual fluctuations of growth for 

 the past 24 years with the climatic record at Flagstaff for that period. 

 Particular importance attaches to the weight of other factors than 

 rainfall and to the determination of the particular months of the 

 year in which occurs the rain of greatest apparent importance in 

 determining the succeeding growth. 



Material for the determination of growth-rate has been secured 

 by the use of a Swedish increment-borer, but the large number of 

 measurements necessary in order to bring together all the data bear- 

 ing on the above problems makes it impossible to state as yet the final 

 conclusions. 



Winter Temperature Phenomena in the Santa Catalina Mountains, 

 hij Forrest Shreve. 



Instrumental readings have been continued on the Santa Catalina 

 Mountains, in connection with other work, with a view to increasing 

 our none too perfect knowledge of the rainfall and temperature 



