18 BOTANICAL GAZETTE [Ly 
mature (stem) wood, and occurs mainly at the ends of the tracheids”’ 
(70) in the livingforms. Some cordaiteans show a notable tendency 
in the same direction. The characteristic paleozoic type of pitting 
is found only in the primitive regions of the living forms (cones and 
roots). 
A torus is present in the bordered pits of all conifers except 
araucarians and some podocarps (70). It is very poorly developed, 
when present at all, in the Araucarineae, and entirely absent in 
Cycadales, Ginkgoales, Cordaitales, Cycadofilicales, and Filicales. 
Miss GERRY (20) has proposed to separate araucarians from 
other conifers on the ground that they lack bars of Sanio in the 
radial walls of the tracheids, which are possessed by all others. 
JeFFrey has gone even farther and held that it is the most certain 
distinguishing feature in separating fossil araucarians from the 
abietineans (35). On the contrary, THomson holds ‘‘that a rudi- 
mentary bar of Sanio is present in all Araucarineae”’ and “‘that the 
araucarians are not to be separated from the other conifers because 
of the lack of a bar of Sanio, but rather that they are to be regarded 
as the basic forms from which this structure in the other conifers 
has been derived”’ (70). I have found no reference to its presence 
in cordaitean wood, so that its absence or feeble os is 
another point of similarity. 
The absence of resin canals in the wood of both Araucarineae 
and Cordaitales is a well known and striking resemblance. THOM- 
SON holds it to be primitive in both cases (70). He brings forward 
much argument to show that resin canals in the pines are primi- 
tively solid, and that they have been derived from resin paren- 
chyma, which has in its turn replaced the resinous tracheids 
characteristic of cordaiteans and araucarians. He concludes that 
‘the origin of the resin tissue of the pine alliance from tracheary 
elements as in the Araucarineae, and the retention of similar stages 
in its development, forms what the writer regards as one of the 
fundamental features of relationship between the two groups.” 
So far as living araucarians are concerned, the cells of the 
medullary rayS are characteristically thin-walled and unpitted, 
just as they are in the Cordaitales. There are known several 
mesozoic forms in which the rays approach the abietinean type. 
