168 BULLETIN L059, U. S. DEPARTMENT OF AGRICULTURE. 



Instruments (Approximate Prices). 



Piche evaporimeter, modifications used by Weather Bureau: graduated to 0.2 

 dc centimeter, capacity about 40 cubic centimeters. Supplied with 



ilate 9 centimeters in diameter, and 1 dozen paper disks. No. 345 6 |6. 50 



Paper disks for evaporimeter, per dozen. Xo. 345 c 





Li >. ; i porous-cup atmometers : 



Natural cups, cylindrical with smoothly ground surface, for general pur- 

 poses -v • )U 



i loated cups, glazed at base, with permanent numbering 60 



Spherical cups, standardized 1. 00 



Shave's nonabsorbing attachment 6. 00 



Foresl Service evaporimeters, equipped with wicks, blackened and calibrated. 1 1. 00 

 Evaporating pans, 10 inches deep, 4 feet in diameter, constructed of No. 22 gauge 

 B. W. G. galvanized iron; can be constructed locally or secured through the I'nited 

 States Weather Bureau. 

 Cobalt-chloride paper slips, "tripartite." 

 • lips, glass, for attaching cobalt-chloride paper to lea 



PHENOLOGY. 



The prevailing idea of ecology as a science through which the 

 mysteries of plant and animal life may be solved merely by measur- 

 ing the environment in more or less exact terms, is gradually giving 

 way to a conception of ecology as a phase of physiology. In the 

 preceding sections it has been attempted to bring out the concept 

 of physiology, at least in its broader aspect, as a basis for those 

 observations and measurements which are commonly associated wit h 

 ecological studies. Unless the nature of physiological reaction- in 

 the plant is understood in a general way, the stimuli which are im- 

 portant to plant life, can not be correctly measured; that is, the 

 environment can not be measured in terms which are expressive. 

 On the other hand, each such effort, by reducing the stimulus to 

 physical terms, permits a little better understanding of the activ- 

 ities of the plant, by placing them more nearly on a physical basis. 

 Thus physiology and ecology must advance side by side, or, bo 

 use a crude simile, like the tread on a caterpillar tractor, in which 

 each segment is in turn brought forward to a point where it may 

 perform its temporary function. 



Now, in fact, phenology is ecology as applied to function- of 

 plants and animals which are more or less regularly periodic or sea- 

 sonal in character. Unfortunately, much good effort has been wasted 

 on phenological observations, particularly in connection with trees- 

 wasted, because no correlation was attempted between the phenomena 

 of growth and any other condition except time, calendar dal 

 Again, effort has been wasted because, while correlation between 

 growth and climatic conditions was attempted, the observations on 



