102 
Yasui. — A Fossil Wood of Sequoia 
Microscopic Organization. 
PI. IV, Fig. i shows a transverse section of the wood in the region of 
a line of traumatic resin canals. The spring tracheides by reason of the 
thinness of their walls have usually almost entirely collapsed as a result 
of the maceration and crushing accompanying fossilization. The summer 
fibres by contrast, on account of the greater resistance to obliteration offered 
by their much thicker walls, are still largely intact. As indicated above, the 
growth rings are rather thin, and the transition from spring to summer wood 
somewhat abrupt. By attentive examination it may be seen that the 
tracheides of the summer wood are provided with tangential pits. The 
‘ resin cells ’ are very prominent, and are scattered through the spring and 
summer wood. The rays are less clearly seen, and as a sequel of compres- 
sion appear as meandering lines always uniseriate. Occasionally dark 
resinous contents may be distinguished in the cells of the rays, similar 
to those occurring in the parenchymatous elements of the wood. In length 
the ray cells correspond to from two to four tracheides. About one- 
third of the distance from the top of the figure appears a tangential row 
of traumatic resin canals, resembling the similar structures in the two living 
species of Sequoia , namely .S'. gigantea and wS. semper virens . As my 
specimen is merely a fragment from a large trunk, it does not show the 
region of actual injury, but the sporadic and abnormal appearance of the 
secretory canals under discussion appears to leave no doubt as to their 
traumatic origin. 
PI. IV, Fig. 2 shows the traumatic resin canals and the surrounding 
cellular elements, somewhat more highly magnified. The resiniferous 
cavities are, as in the case of the species of the living genus, surrounded by 
secretory cells, which are to a very limited extent characterized by the dark 
brown contents, which mark the so-called ‘ resin cells ’ of the wood. The 
resiniferous elements, in fact, in the case of traumatic resin canals in both 
living and extinct species of Sequoia are comparable rather with the resin- 
secreting cells surrounding the resin ducts of the wood of the Abietineae, 
than with the longitudinal parenchymatous strands of Cupressineous woods. 
Certain of the short cells in proximity to the resin canals are neither 
resiniferous elements nor ‘ resin cells ’, but are short tracheides of the type to 
which Penhallow gives the name ‘ parenchyma tracheides \ They in fact 
correspond very accurately to the structures shown in Text-fig. 40 in his 
‘North American Gymnosperms V Attentive examination of this figure 
shows the bordered pits in the transverse end walls of cells of this type. 
PI. IV, Fig. 3 illustrates the radial view of the wood under discussion. 
In the centre the abundant parenchyma (only a small part of which consists 
1 Penhallow, D. P. : North American Gymnosperms, Boston, 1908, Text-fig. 40, p. 126. 
