450 



EDWARD C. JEFFREY ON 



after the leaves have emerged from the surface of the branches, so, as has just been stated 

 above, the longitudinal course of the resin canals of the leaf traces, where they occur, is 

 very short indeed. 



The Stem of Sequoia sempervirens. 



Penhallow (op. tit.) has noticed the occurrence of continuous tangential rows of 

 what he terms "imperfect resin ducts" in the wood of the old stem of S. sempervirens. 

 The phenomenon seems to be extremely rare, for I have found very few examples 

 although a large number of different specimens of the wood of this species has been 

 examined in this connection. Professor Penhallow has been so kind as to send me a 

 very good example illustrating this peculiarity, and as it is much more striking than any 

 other I have seen, all the accompanying figures of the mature wood of S. sempervirens 

 are made from this material. In figure 24, plate 70, a part of a transverse section of the 

 wood of 8. sempervirens is represented under a low magnification. There are four 

 annual rings present in the figure. Mingled with the tracheids in all the four woody 

 rings are numerous resin cells, such as have been described above in 8. gigantea, and 

 such as occur commonly in the other Taxodineae. The autumnal wood in 8. semper- 

 virens forms a much thicker zone than in 8. gigantea, which is the cause of the greater 

 weight and strength of the wood in the former species. In the second annual ring from 

 the top of the figure are to be seen the resin ducts first described for 8. sempervirens by 

 Penhallow (op. cit., p. 39, pi. 6, fig. 2) . They are obviously situated in the autumnal 

 wood and in this respect present a marked contrast to those of 8. gigantea described 

 in the foregoing paragraphs, for in the latter species they occur in the vernal portion of 

 the annual ring. In their distribution the resin canals in the present instance resemble 

 those formed as the result of injury in 8. gigantea, species of Abies, etc., and form a 

 continuous tangential zone, such as is characteristic of traumatic resin canals. Figure 

 25, plate 71, shows a portion of the annual ring containing resin ducts more highly 

 magnified. There is obviously a sharp transition from the autumn wood to that of the 

 following spring in the size of the tracheids and the thickness of their walls. There are 

 numerous resin cells on the outer margin of the autumnal wood. Farther inwards, the 

 autumnal tracheids give place to parenchyma cells, which, on account of the fact that 

 the material is from the heart wood of an old tree, are quite devoid of protoplasmic 

 contents. They are unmistakable, however, since their walls are composed of cellulose 

 and stain a deep blue with haematoxylin. About the lumina of the resin ducts, the 

 parenchymatous cells are as a rule strongly pitted and closely resemble the resin cells 

 of the medullary rays in certain Conifers. 



