1915] BROW N—PINUS STROBUS 201 
Investigations on the roots of trees were attempted and gave 
some results worth noting. The roots were secured from young 
trees (about 30 years). Other root studies were made on seedlings 
from the nursery. A few cuttings were taken from the roots of 
old trees where they were exposed near the base of the bole. 
Microscopical characters of the xylem 
The xylem of white pine is so well known that it is unnecessary 
to describe it here. When contrasted with the wood of pitch 
pine, the xylem of white pine differs in a number of anatomical 
features. The upper and lower walls of the ray tracheids are 
smooth as compared with the dentate ones of Pinus rigida. 
Bordered pits occur on the tangential walls of the late wood, while 
they are lacking apparently in pitch pine. The transition between 
early and late wood is not so abrupt in white pine and the rings are 
generally wider. White pine is a more thrifty tree, and the present 
observations tend to show that it is more susceptible to changes 
of site, soil, etc., than pitch pine. This is exceedingly important 
from the economic standpoint. 
The roots of white pine exhibit the usual features of the roots 
of Abietineae. Diarch, triarch, and tetrarch roots are common. 
The’ root of seedlings is usually diarch (fig. 8), but the number of 
xylem rays is as a rule soon increased to three or four. Vigorous 
roots from thrifty trees between 15 and 30 years of age were pre- 
vailingly tetrarch, so that it would appear as if the number of 
xylem rays is correlated in some way with the amount of moisture 
available to the root and to the root environment, whether favorable 
or otherwise. VAN TreEGHEM (34) has noted this same variability 
in Pinus, Abies, and other allied genera, and further has pointed 
out that no constant relation prevails between the number of 
xylem rays and the number of cotyledons. Not only does the 
number of xylem rays vary in roots of different ages, but the 
number may increase or decrease during the growing season. This 
is strong evidence that environmental conditions influence within 
3Each xylem ray is terminated centrifugally by a resin canal, and the oli- 
garchy of fey roots can in this way be easily determined in cross-section with 
the naked e 
