Barber . — Cupressinoxylon vectense. 
352 
Measurements of Tangential Pits . 
Branch (1). Average of 36, outer diameter 5 [x, inner 2-35 /x. 
Branch (2). Presence easily noted, but not sufficiently clearly for accurate 
measurements. 
Root (1). Average of 26, outer diam. 7.3 fx, inner 2-3 jx. 
Root (2). Structure of wall not well preserved : tangential pits not met with. 
The numbers of rows of summer tracheides in each ring 
bearing tangential pits have been carefully determined for 
recent Conifers, and the different groups are seen to vary 
considerably in this respect. Kraus recommends observa- 
tions in transverse sections, but it is only possible in our 
sections to use the radial ones. In the latter the tangential 
pits are sometimes very clear. The section of the pit has 
the form of a sharply cut lens-shaped space, and not in- 
frequently the torus is found stretched across it as a short 
black line. In other cases this space is without the torus. 
In a third set of examples the lumen of the pit is filled 
up by infiltration, but the torus is well seen as a short black 
line in the thickness of the wall (cf. Figs. 11-13). These three 
conditions are often found close together, all manner of 
transitions being seen. It becomes quite possible then, after 
careful study, to make out the tangential pits in comparatively 
thick sections with the help of a substage condenser. This 
has been of the greatest service in counting the number of 
rows of summer-tracheides with these pits, because this part 
of the wood is generally very dense. 
The observations have been most successful in branch (2). 
Here the tangential pits are sometimes found in the last 
seven rows of tracheides. This abundance of tangential pits 
is in agreement with the other characters of our fossil wood, 
showing us that in the Cretaceous period, where Cupres - 
sinoxyla are first met with 1 , the type of wood found in 
Cupressus , Sequoia and Abies was developed in its minutest 
details. In Abietinae with composite medullary rays these 
1 Schenk in Zittel, 1 . c. 
