1909] BAILEY—STRUCTURE OF WOOD IN PINEAE 49 
developed spiral thickenings in the spring as well as the summer 
tracheids. Further, according to Mayr,; spirals are also present in 
the ray tracheids of Pseudotsuga macrocarpa Mayr, but not in P. 
Douglasii Carr. 
With this review of the generally accepted classification of the 
Pineae, let us turn to a careful consideration of the occurrence of each 
of the anatomical characters referred to above. In the first place 
as regards 
WOOD-PARENCHYMA 
As stated above, these cells are supposed to exist on the outer sur- 
face of the summer wood in Larix and Pseudotsuga, and to be entirely 
absent from Pinus and Picea. The presence of wood-parenchyma 
on the face of the summer wood in the xylem of a specimen of Picea 
excelsa Link in the Harvard Botanical Gardens led me to study this 
tree, believing that it was an unusual or freak specimen. The exami- 
nation of sections from the root and stem showed the parenchyma 
well developed at the end of the year’s growth (figs. 1-3), but in many 
cases the parenchymatous cells were rare or apparently absent from 
the stem. However, numerous sections cut from the same piece of 
wood always revealed one to several cells. It-is difficult to see them 
in a transverse section, as they can be distinguished with certainty only 
when the simply pitted walls are visible. Obviously, to obtain this 
condition when the cells are rare is difficult. Likewise, in radial sec- 
tions it is not easy to find them. If, however, tangential sections are 
cut in a slightly oblique manner, several layers of summer wood are 
visible in a single section. Many sections cut in series would then be 
more liable to reveal the presence of parenchymatous cells even when 
occurring infrequently. Cutting the sections in series avoids the 
possibility of confusing the parenchyma, for which I was searching, 
with that associated with resin canals or wound callus. However, 
the appearance of the latter as well as their location (not confined to 
the outer layer of the summer wood) is sufficient for their identification 
without these precautions. 
I decided to use this method in the examination of other specimens 
of Picea excelsa, to see if wood-parenchyma were characteristic of the 
species. Upon examination it was found that the cells were present 
5 Mayr, Die Waldungen von Nordamerikas 424. pl. 9. Miinchen. 1890. 
