102 
Journal of Agricultural Research 
Vol. XXIV, No. a 
opposite direction. Such variations from a consistent relation are, how¬ 
ever, always small, and there is every reason to believe that the means 
of a single month usually express essentially the normal temperature 
relation between two stations for that month of any year. 
Therefore the method of study and the method of presenting results 
is that of comparing each factor for any station with the corresponding 
factor at the control station for whatever period observations may have 
been taken at the outlying station. As a basis for this comparison we 
have the record of each factor* at the control station, measured with 
practically no variation in method from January, 1910, to date. Excep¬ 
tion should be made here to the measurement of evaporation, in which 
a satisfactory method was not attained until 1917. 
The detailed methods of taking meteorological observations, so far as 
they vary from the standard methods of climatologists the world over, 
will be described in connection with each condition measured. 
REVIEW OF OTHER WORK AEONG SIMILAR EINES 
Although much systematic ecological study has been attempted in the 
United States and other countries, and the western portion of our own 
country has offered an especially attractive field for ecologists because 
of the sharp contrasts in vegetation and causative factors which are 
found in relatively small areas, still the main field with which foresters 
are concerned has barely been scratched. Several studies, which might 
have been very productive, scarcely satisfy the forester's requirements 
because of the lack of long-term records. 
Be that as it may, a number of authors have obtained facts and 
deduced conclusions as to the distribution of our Central Rocky Mountain 
forest trees which we can not afford to overlook. No attempt will be 
made at this stage to introduce these facts, which may better be men¬ 
tioned in connection with my own discussions and conclusions. I shall 
merely list here the works which have a direct bearing on the major 
problems, and with no attempt to cover the general or specific physio¬ 
logical studies. 
Clements (7, 8 , 10) in three of his works presents many valuable ideas 
regarding the relation of Rocky Mountain vegetation to environmental 
conditions, and with particular reference to the Pikes Peak region, in 
which much of his investigation has been conducted. The latest of 
Clements’s books, “Plant Succession” (ro), published in 1916, may he 
said to cover the entire ground of the earlier works, bringing all of his 
observations under one comprehensive theme, namely, the changes 
which occur in the character of the vegetation of a ^ven area as flie 
result of reactions of the plant forms upon the environment and of 
gradual changes in the climatic and edaphic (soil) conditions. 
In a more specific work Clements (9) gives to foresters a much more 
concrete idea of the requirements of an important tree species, lodgepole 
pine, with lesser data on its common associates. 
Ramaley (16, 17), working near Boulder, Colo., and in the deeper 
mountains at Boulder Park, has likewise made numerous observations 
on the forest types and zones of Colorado. His papers, however, make 
no claim of extensive systematic measurement of physical factors and 
hence can be considered as having only suggestive value in connection 
with the present work. In both of the papers cited the theme is a classi- 
