442 



EDWARD C. JEFFREY ON 



autumnal tracheitis form a very narrow zone in each annual ring of growth, and the 

 wood consequently lacks the strength which is characteristic of the latter species. The 

 radial rows of tracheids are interrupted at intervals, especially in the autumnal region, 

 by the resin cells which are so constant a feature of the wood of the Taxodineae and 

 Cupressineae. As has been pointed out by Penhallow (Generic characters of North 

 American Taxaeeae and Coniferae, Proc. and trans, roy. soc. Canada, 1896, series 2, vol. 

 2, p. 33), the resin ducts, found so frequently in the wood of the Abietineae, are absent in 

 the mature ligneous cylinder of 8. gigantea. Figure 2, plate 68, gives a general view of 

 the central cylinder of a branch of a young tree from the arboretum of Leland Stanford 

 university, California. The stem is a year old and shows as a consequence a single ring 

 of wood. The resin cells of the wood are poorly developed as yet, although those of the 

 phloem are very apparent in spite of the comparatively low magnification. The minute 

 structure of the fibrovascular tissues cannot be made out. 



Figure 3, plate 68, is of the central cylinder of a five year old branch of S. gigantea 

 taken from a tree which had already produced cones and seeds. The autumnal wood is 

 relatively much thicker than in the old stem shown in figure 1. The feature of special 

 interest in this section is the presence of resin ducts in the inner region of the first 

 annual ring. Figure 4, plate 68, shows the first annual ring and the resin ducts more 

 highly magnified from another section, cut from a different twig of the same main 

 branch. As the material came from the Gray herbarium of Harvard university and 

 was consequently in a dried condition, the cells surrounding the resin ducts show no 

 evidence of the presence of protoplasm and a nucleus ; but the obviously resinous con- 

 tents of the ducts in the dry condition, as well as the parenchymatous nature of the cells 

 surrounding them, leave no doubt as to their identity. In the last mentioned figure, 

 the cells enclosing the lumen of the resin canals appear darker as to their walls than the 

 adjacent tracheids. This is due to the fact that they become stained very intensely with 

 haematoxylin, and thus are more non-actinic than the surrounding tracheids, counter- 

 stained less strongly with aqueous saffranin. The material presenting these peculiarities 

 in the first annual ring was taken from specimens accompanied by unusually large cones, 

 and labeled " J. G. Lemmon, California." In order to test whether the structures in 

 question were not abnormalities, sections were made from two other lots of material 

 from the Gray herbarium, marked " Bridges 331 " and " Henry 1086," respectively. 

 Figure 5, plate 68, shows the central portion of a transverse section from the material 

 marked " Bridges 331." The resin ducts are obviously even better developed than they 

 are in figure 3. Sections from the other lot of material also showed the presence of 

 large and typical resin ducts in the first annual ring of the wood. The resin passages 

 just described disappear in the upper part of the annual ring as it reaches what was 



