GENERAL REPORT. 37 
Of course, the question as to how long we must wait for these trees to 
develop into timber is another element of the problem, and this will vary 
with the particular species of tree. In California, we might expect the blue 
gum would in five years be large enough to use as fuel and as fencing, but 
we could hardly expect -it to have sufficient girth to answer most commer- 
cial purposes inside of thirty years. Emerson, in his ‘Trees and Shrubs 
Growing Naturally in the Forests of Massachusetts”, instances a white pine 
planted near. Paris thirty years before, that had attained a diameter of 3 
feet and was 80 feet high. Marsh, in “‘Man and Nature”, p. 274, tells of 
another that in thirty-six years had grown to 25 inches in diameter. The 
Ailanthus, American elm, and chestnut may be given as illustrations of 
rapid growth. Either of these would in thirty years produce good timber. 
The Nevada and Utah districts have been so thoroughly elaborated by 
Mr. Watson in Vol. V. of King’s Reports, that no further statements con- 
cerning them are requisite. There is also an able article by Dr. W. J. 
Hoffman on the distribution of vegetation in portions of Nevada and Ari- 
zona, in the American Naturalist for June, 1877. Dr. Hoffman’s former 
connection with this Survey, his opportunities for observation, and his zeal 
in botany, confer a special value on his paper. 
I am indebted to my friend Dr. George Martin, of West Chester, Pa, 
for the following important note: 
Mean annual rainfall in parrots Fey for 43 years, i. e., from 1825 to 1867, 
inclusive.... .- ee . 44.02 inches. 
Thus, mean for the first sores, 214 years, ot this period. seevne ents tues oe 42.12 inches. 
For the second series of the above period .. et bs peek~ buses ne aol ee AORIOR. 
Taken from Smithsonian Tables (May, 1872). 
Mean annual rainfall in West Chester, Pa., for 18 years, 7. ¢., from 1860 to 
BATT, WOCUOAI VO. ooo gon wks seme oa got o> ose snes seses covers sen ebs 51.18 inches. 
Thus, mean for the first series of 9 years of above period.......- . 50.16 inches. 
For the second series of same period... ..-.---- eee cee eens cee eee 52.20 inches. 
Taken from Register of Dr. Jesse C. Green. 
All will admit that a large body of woodland has been cleared during these periods 
in the vicinity of both these stations, and yet there has been an increase in precipitation. 
It will not do to compare the observations taken at West Chester with those of 
Philadelphia unless the whole series could be taken, as the local influences and errors 
of instraments have not been eliminated. Each, however, is complete and conclusive 
in itself. 
