202 BOTANICAL GAZETTE [MARCH 
certain limits the number of xylem rays. In general the larger 
the diameter of a yearling root, the greater the number of rays up 
to four. A pentarch or hexarch arrangement was not observed 
in any case, although it may occur, since VAN TIEGHEM (op. cit. 
p. 7) reports the number as high as 7 in Scotch pine (P. silvestris). 
The xylem in old roots is comparable to that in the aerial parts 
of the tree, but differs in several well known particulars. . The 
tracheids in roots have wider lumina and thinner walls and are - 
never as well lignified as those in the parts above ground. This is 
especially well seen in cross-sections. In roots late wood formation 
is not as pronounced, owing no doubt to a decrease in mechanical 
strain in underground parts. The bordered pits on the tracheid 
walls, in both roots and stems, are mainly radially arranged. The 
uniseriate arrangement is here and there interrupted by the pairing 
of some pits. Further, the bordered pits in roots are larger than 
in the xylem of aerial parts. It is of interest to note in this connec- 
tion that wherever an old root becomes exposed it usually presents 
xylem typical of aerial parts, so that only underground parts 
exhibit the characteristics above described.* 
Winter condition of secondary cortex and cambium* 
The secondary cortex of white pine is very similar to that of 
pitch pine. It presents the same radial arrangement of the ele- 
ments, this arrangement becoming less regular as they are pushed 
to the outside (fig. 1). Companion cells are totally lacking, but 
one distinct row and a few scattered bast parenchyma cells are 
formed each year as in pitch pine, and these indicate the annual 
phloem areas in the old cortex. Occasionally the phloem pa- 
renchyma becomes crystallogenous, but never attains the size of 
that of pitch pine. The marked differences which exist between 
the bark of white pine and pitch pine are not present in the young 
phloem, but are caused by changes which take place subsequently 
in the outer cortex. 
4 Kny (20) has pointed out the same structure in P. silvestris, and found that it 
was especially pronounced on the underside of large roots which had been exposed 
rough erosion. 
5 The notes only include observations on the winter condition of aerial parts, 45 
underground parts were not accessible at this time of the year. 
