28 BOTANY. 
shall reach. Hence it does not surprise one to find the lowest limit of 
Coniferous vegetation ranging somewhat in this manner as one goes south: 
Feet 
Nouth Park, Colorado oo 6.s.% 5252 e tans s a pe ase ee a rik wks 9,000 
od Ee gE eee eee re re ere eeme 7,500 
auee +6, ew Menten (PinOn) bss sa ec s cece seg eee e ees es 7,100 
Wart. yma, Dew Mexico (Pifion) . ......0 sak Caen e bee nek 7,000 
Mogollon Mesa, Arizona (Pinus ponderosa) ............- ies fies 6,500 
Pn ti, ITA TOI) og och. Sane cu ene e a neces 6,200 
Ne Nr ei CO a ee ae ee ek 5,000 
Camp Grant, Arizona (Pinus ponderosa) ....-....-.-. w+. eee. 6,500 
Camp Crittenden, Southern Arizona (Oak).. cate 4,749 
Camp Crittenden, Southern Arizona (Pinus poallereaa). vbakes we 5,500 
In other words, where the plain breaks up into a well-defined mountain 
range or peak which is well watered, the timber begins just above the limit 
of the plain. 
The upper limit of forest growth, or, as it is called, ‘“timber-line,” is 
less clearly defined. Dr. Engelmann has clearly pointed out, in “The Trans- 
actions of the Saint Louis Academy of Science” for 1862, p. 129, that near 
Denver it begins just at about the altitude it disappears in Alpine Europe; 
in other words, that it ascends in our Rocky Mountain Range about as high 
above the great plain out of which these mountains rise as it does on the 
Alps above the ocean level ; and the conclusion appears clear that this plain 
receives the heat freely during the day, and its dry air allowing as ready a 
radiation of it at night, it (the plain) becomes the furnace whose heat is to 
carry the timber to so unusual an altitude. 
Dr. Engelmann further notes that the popular opinion that this upper 
limit is carried to greater altitudes as we go south is not correct The 
following table may throw some further light upon his statements. 
The upper limit of trees averages between— 
Latitude 40-41° north, 7 peaks. .. 
pate h crs cee ee ET Pe. 
Latitude 38-409 north, 15 peaks. : 0.00. s. 2. ooo s see ccccccee cs 11, 636 
smtitode 38-30° north, 6 néaks...2:. ©. 2,35. 11, 729 
PORIEORG SI-OR? BORED, DS POGKR oi. s oo ooo os iss ee sc 10, 625 
San Francisco Mountains, 35-369, latitude north .............. 11, 547 
*Sierra Blanca, Arizona, 33-349, latitude north .. ............. 11,100!! 
*A portion of the material for this table I have obtained from Mr. Gannett’s admirable ‘ List of 
Elevations” —a paper of great labor and great value 
