Ray Tracheitis in Sequoia sempervirens. 
3 
elongated ray tracheids. These vary in radial extent, are two to 
two-and-a-half times as high as the parenchymatous cells of the 
ray, and have irregular walls. They are similar to the “ transitional ” 
tracheids of the young root and young stem of the pines (Thompson, 
1910, Fig. 11). They do not, however, as in the latter group, give 
rise to the normal ray tracheids if the rays between which they 
occur separate farther, whereas in the pine this has been shown to 
be an ordinary method of formation of marginal ray tracheids. 
Inasmuch, however, as they resemble in form and position these 
so-called “ transitional ” tracheids of the pines, they are of a 
primitive type. 
There is thus in noth marginal and interspersed ray tracheids 
of S. sempervirens much variability in form. Gothan (1905) has 
called attention to the variability in form of the ray tracheids in the 
other species of Sequoia, which he compares to those of Picea and 
Larix, but which he states are not so abnormal as those of Thuja 
gigantea, as figured by Mayr (1890). Gothan, however, did not 
figure those of S. gigantea. 
Fig. 3 
Fig. 4 
So far we have described the ray tracheids from the standpoint 
of size and form, and have noted certain differences in these features 
between them and the parenchyma cells. These features, however t 
do not give us sufficiently definite and accurate data by which to 
distinguish the two constituents of the ray, and in practice the 
pitting was made the criterion. It affords a ready and absolutely 
reliable basis. The radial pitting is especially serviceable, as seen 
in face view in the radial sections, which were found most adapted 
to this study. The pits thus seen (Figs. 1-3) are quite small but 
rather variable in size. Ordinarily they are not more than half the 
diameter of those where a tracheid touches a parenchymatous ray 
cell. These in turn are much smaller than the ordinary pits of the 
tracheids themselves (Figs. 2 and 3). In form, too, these three 
types of pits differ. The ordinary medullary ray cell pit is oval, and 
its border is confined to the upper and lower margins. This border 
