218 BOTANICAL GAZETTE [SEPTEMBER 
in radius, but was occasionally noted where it amounted to 38™™ 
(r.5™). Such a constriction is often seen on individual trees in 
nearly any stand, but in no other case was it found to be a stand as 
characteristic as it was near Servilleta. 
Pifion is also resistant to severe climatic conditions, since it will 
succeed over severely exposed slopes where the average annual 
precipitation is less than 33°™ (13%) and where evaporation and 
transpiration are high because of the semi-arid climate, the large 
amount of sunshine, and the prevalence of winds. In this respect 
it is undoubtedly the most resistant pine in the southwest. However, 
it prefers a slightly greater precipitation and areas less exposed to the 
wind. An example of the unfavorable influence of strong winds and 
a Close-textured soil was noted in the vicinity of Fort Stanton, New 
Mexico, where a level plateau of nearly 8" (5 miles) in length did 
not support a single tree, while similar plateaus on all sides, with less 
wind sweep and a coarser soil, showed luxuriant growth of both the 
pifion and the juniper. The tree does not live as long as the junipers, 
and in general is less resistant to unfavorable climatic conditions. 
In the drought which occurred in New Mexico from 188g to 1904; 
pifion suffered considerably more than the junipers. Many mixed 
stands were observed in New Mexico and southern Colorado in 
which 75 to 95 per cent. of all dead trees were pifion. In the frost 
which occurred in April, 1907, pifion was affected, while the junipers 
resisted practically all injury. In the wet freezing snow of October, 
1906, which caused immense damage to the forests of the southwest, 
fewer branches were broken from the pifion than from the brittle 
junipers. 
The tree is also more resistant to disease than most of the conifers 
with which it associates. It is much less affected by the so-called 
false mistletoe (Razoumofskya) than is the western yellow pine and 
the junipers. It has fewer insect enemies than the western yellow 
pine, and is not affected by the witch’s broom as is often the case 
with Douglas fir in the southwest. 
TOLERANCE AND FORM 
Pifon is distinctly an intolerant tree. During its seedling — 
it prefers a moderate shade, and hence reproduces best under thé 
