168 BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE. 
Instruments (Approximate Prices). 
Piche evaporimeter, modifications used by Weather Bureau; graduated 
to 0.2 cubic centimeter, capacity about 40 cubic centimeters. Sup- 
plied with glass plate 9 centimeters in diameter, and 1 dozen paper 
disks, No. 345 & $6.50 
Paper disks for evaporimeter, per dozen, No. 345 c .25 
Livingston porous-cup atmometers : 
Natural cups, cylindrical with smoothly ground surface, for general 
purposes . 50 
Coated cups, glazed at base, with permanent numbering . 60 
Spherical cups, standardized , 1. 00 
Shire's nonabsorbing attachment 6. 00 
Forest Service evaporimeters, equipped with wicks, blackened and cali- 
brated , 11. 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 United States Weather Bureau. 
Cobalt-chloride paper slips, " tripartite." 
Clips, glass, for attaching cobalt-chloride paper to leaves. 
PHENOLOGY. 
The prevailing, idea of ecology as a science through which the 
nry steries 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 with 
ecological studies. Unless the nature of physiological reactions 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 busis. 
Thus physiology and ecology must advance side by side, or, to 
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 functions 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 dates. 
Again, effort has been wasted because, while correlation between 
growth and climatic conditions was attempted, the observations on 
