2 
Marjorie Gordon. 
cells are considerably shorter than the one figured. Fig. 2 shows 
a vertically elongated one. It also has a very irregular margin, but 
in radial extent covers only from one to one-and-a-half tracheids, 
while in vertical extent it is fully twice as high as the parenchyma 
cells of the ray. The height of the latter is quite uniform, and the 
cells have also very regular walls. 
These elongated marginal ray tracheids recall some of the 
structures found in the pine by Thompson (1910, Fig. 13), which 
structures he considered of a primitive type ; and though in Sequoia 
no forms intermediate between the vertically elongated and the 
normal radially elongated ones were found, these vertically elongated 
structures are quite comparable to those of the pine, and are capable 
of a similar interpretation. Other marginal ray tracheids were 
found with sac-like projections from the end towards the cambium : 
these “ tailed ” ray tracheids have also their counterpart in the pine, 
chiefly in young root-wood, where Thompson states that the tails 
“ seem to be due to an incomplete shortening of the tracheid as it 
turns along the ray” (p. 108), considered by him a vestigial feature 
in the process of ray tracheid formation from ordinary vertically 
arranged but short tracheary elements. 
These various forms of ray tracheids occur on both sides of the 
medullary rays, not forming a definite row, but scattered along the 
rays. Sometimes they are found wholly in the spring wood (Fig. 3), 
but more often at the annual ring, the main part of the tracheid 
lying in the spring wood, but with a small part extending into the 
fall wood (Figs. 1 and 2). 
The interspersed ray tracheids are similarly situated. Fig. 4 
shows a radially elongated one. It extends over only one-and-a-half 
spring tracheids; but longer forms are quite common. Usually 
these cells aie slightly less in height than the adjacent parenchyma 
cells (see Fig. 4). They are regular in outline, and although they 
closely resemble the ordinary ray cells in form, the pitting, as will 
be seen later, is very different. Fig. 5 shows two vertically 
