. A manual of the North American gymnosperms [microform] : exclusive of the cycadales but together with certain exotic species. Bois; Trees; Gymnosperms; Gymnospermes; Arbres; Wood. SPIRAL TRACHEIDS latter case, however, the spirals are either sporadic anH estigial P. Douglasu) or they are often almost completely obliterated P. macrocarpa). So well defined and constant are these relations that they serve as an important differen tial character for the genus. Tracheids with spirals developed in the tertiary layer of the wall are thus seen to be typical features of Taxus, Torreya, and Pseudotsug
. A manual of the North American gymnosperms [microform] : exclusive of the cycadales but together with certain exotic species. Bois; Trees; Gymnosperms; Gymnospermes; Arbres; Wood. SPIRAL TRACHEIDS latter case, however, the spirals are either sporadic anH estigial P. Douglasu) or they are often almost completely obliterated P. macrocarpa). So well defined and constant are these relations that they serve as an important differen tial character for the genus. Tracheids with spirals developed in the tertiary layer of the wall are thus seen to be typical features of Taxus, Torreya, and Pseudotsuga, while they are also more or less distinctive features of Larix ameri- cana and Pinus tzeda. In all investigated species of Torreya there is a rather wide variation in the angle which the spirals make with the axis of growth, and this becomes most pronounced in T. califomica, which gives the lowest angle for any species of either Torreya or Taxus. Usually the spiral has an angle quite distinct from that of the lines of striation in the cell wall, but in Torreya taxifolia (fig. i) the two often coincide. The following will show the various details derived from the average of ten measurements for each species-. Fig. I. Torreya TAXIFOLIA. Radial section showing spirals of tracheids and bordered pits, x 210 Average Angle Highest Angle Lowest Extreme Range Torreya nucifera . Torreya taxifolia . Torreya califomica . ° ° 770 57-0° 30-0° 330 Means ° 75-7° 49-3° ° In the genus Taxus (fig. 2) the spirals are rather close and in two, ^rely three, series. As in Torreya, they are typical throughout the spring wood, but with a pronounced tendency to obliteration m the summer wood. This tendency is subject to considerable. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work
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