Apr. 14, 1923 
Physiological Requirements of Rocky Mountain T rees iii 
All observations were made in the early morning and before sunlight 
had reached the trees, and when, therefore, the transpiration rate would 
be almost at its minimum. The order of measurements was invariable^ 
and the time rarely varied more than 15 minutes from the standard. 
Now, in fact, though it has been stated that the plan was to maintain 
standard moisture in each can, it is readily seen that the moisture was 
most of the time below standard. The extent of the ordinary depressions 
was very small. The largest single loss between fillings, 15 7.1 gm., 
would mean a moisture content at the end of the period of 13.9 per cent, 
or a depression of 6. i per cent. The average periodic loss of the heaviest 
water-ttser was 23.76 gm., and the average depression below standard 
moisture, therefore, only 0.93 per cent. This average depression would 
reduce the availibility of the moisture only from the approximated value 
0.852 to 0.846. 
On the other hand, the distribution of the moisture from top to bottom 
of each pot, as shown by examination at the end of the tests, was not all 
that might be desired. The lowest inch of soil was practically saturated, 
and above this the moisture decreased so that just below the paraffin 
the soil was only freshly moist. In spite of this, rootlets had penetrated 
to all sections of the soil. It seems evident that, except with the most 
extreme depletion noted, there was probably within reach of the longest 
roots at all times practically saturated soil. 
The atmospheric conditions of the greenhouse, as has been stated, were 
not such as would occur naturally in any of the sites where these species 
grow. At times the ventilators were kept closed and the air temperatures 
were allowed to go as high as they would with full sunlight. At o^er times 
the ventilators were opened and all possible draft was developed; and, 
of course, under these conditions the air of the greenhouse did not become 
so warm. Again, sunlight was excluded on certain days to see what 
effect this would have on transpiration rates. On two or three occasions 
when cloudy weather prevailed, an interval of 2 or 3 days was allowed to 
elapse between measurements, since the losses were very small. On two 
occasions when the writer was not there to make the measurements, the 
intervals were considerably longer, the trees being shaded by canvas for 
the entire period. 
No apparent injury resulted from the high temperatures in the green¬ 
house, except to tree No. 4, Douglas fir. On June 24, which was a clear 
day of exceptionally low humidity and high evaporation rate, two of the 
newly formed shoots on this tree wilted and did not recover. Neverthe¬ 
less the tree continued to function properly. The other Douglas fir 
(No. 3) followed No. 4 very closely, but after the first of September 
showed a gradual descrease in its response to transpiration stimuli and 
when unpotted was found to be deficient in new root growth. In the 
normal trees it appeared that many of the root tips had continued growth 
to the end of the season, while in this one growth had evidently ceased 
much earlier. 
Tree No. 10, limber pine, at the end of the season showed very short 
growing tips on the roots, indicating that root development had been 
very sluggish or had started very late. This sluggishness is doubtless 
related to the small weight accretion. 
