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Igog| BAILEY—STRUCTURE OF WOOD IN PINEAE 55 
4. Septate tracheids occur in Pinus, and wood-parenchyma very 
rarely. 
5: Spiral thickenings of the tracheids occur in both the spring and 
summer wood in Picea and Pseudotsuga, and occur in the summer 
wood of Larix. These thickenings occur also in Pinus. 
6. Spiral thickenings of the marginal and interspersed tracheids 
of the rays occur in Pinus, Picea, and Larix, as well as in Pseudotsuga. 
7. The anatomical characters of the wood are so variable and so 
similar in Picea, Larix, and Pseudotsuga, that it is difficult to distin- 
guish the extant or fossil woods of the genera. 
8. Pinus appears to be quite distinct from the other living Binena 
Yet in the nut and foxtail pines, we see a condition resembling the 
condition in Picea, Larix, and Pseudotsuga. These pines have small 
rounded pits in the ray cells, have tangential pits like Picea, have 
thick-walled epithelium in the canals, and spiral-thickenings in the 
ray tracheids. 
g. Picea approaches nearer to the condition in Pinus by having 
more numerous thin-walled epithelial cells and tyloses, and less well- 
developed wood-parenchyma; yet Larix and Pseudotsuga also have 
thin-walled epithelial cells occasionally, and may have the wood- 
parenchyma poorly developed. 
HARVARD UNIVERSITY 
CAMBRIDGE, Mass. 
EXPLANATION OF PLATE V 
Fic. 1.—Transverse section of stem of Picea excelsa, showing four resin cells 
on the outer face of the summer wood. X500 
IG, 2.—Radial section of root of Picea excelsa, showing resin cells on the 
outer face of the summer wood. X 180. 
Fic. 3.—Tangential section of root of Picea excelsa, showing resin cells. 
80. 
Fic. 4.—Radial section of root of Picea excelsa, showing tracheid partly 
septate and border-pitted, and partly parenchymatous and simply pitted. X 180. 
Fic. 5.—Radial section of stem of Picea Maximowiczii, showing spiral thick- 
enings in the marginal tracheids. goo. 
Fic. 6.—Tangential section of stem of Picea Maximowicsii, showing spiral 
thickenings in both the spring and summer wood. X 180. 
