1 1 8 
Slopes. — An Early Type of the 
in slides 51488 and 51724, the thickening and ‘ Abietinean pitting ’ of 
a number of the medullary ray cells can be clearly seen. Some sketches 
from these are given in my Text-figs. 5 , 6 , and 7 . 
At the time Seward wrote ( 1904 ) the diagnostic importance of the 
medullary ray cells was not fully realized, and he gives no figures of 
the details of their walls. Regarding the rays, he says : ‘ Medullary rays 
distinct in transverse section of the wood, composed of narrow, radially 
elongated cells, with single pits in their walls ; the rays vary in depth from 
a single row to more than twelve rows of parenchymatous cells.’ Further 
on he says of the rays that ‘ they consist of radially elongated parenchyma- 
tous cells which occasionally exhibit small pits, and the cavities are often 
Text-fig. 6. Planoxylon Lindleii (Witham). 
Cells of medullary ray in radial view, showing 
the thickening and 4 Abietinean pitting ’ of all 
the walls. [From Slide No. 51488, British 
Museum (Nat. Hist.).] 
Text-fig. 7. Planoxylon Lindleii 
(Witham). Sketch from a part of 
Section No. 51724, British Museum 
(Nat. Hist.) Geological Collections, 
to show the outline of the cells of two 
medullary rays with the irregular 
terminal cells suggestive of the Abie- 
tinean feature of ray tracheides. 
full of vacuolated brown contents.’ The radial view of the medullary ray 
cells given by Witham is merely a series of straight lines. It is therefore 
necessary now to describe the detailed character of these cells. 
In a few cases in transverse sections, I have seen portions of the top and 
bottom walls in surface view similar to those described in the New Zealand 
specimen and figured in Text-fig. 1 , mp. In the tangential sections also, 
e. g. in slide 51486 (British Museum), faint suggestions of these pittings can 
be seen. But in a number of places the radial sections retain quite clearly 
the thickening and pitting of the ray cell-walls. A typical ray is sketched 
in Text-fig. 6 from slide 51488. Here the characteristic thickening and 
