492 
Stiles . — T he Podocarpeae . 
with a single functional resin canal on the under side. In the leaves of 
Podocarpus macrophylliis and similar ones, the effect of increase in size has 
probably rendered necessary the development of the accessory transfusion 
tissue for strengthening purposes. In the larger single-nerved leaves also 
the single resin canal is replaced by three smaller ones. If Bertrand’s 
description is correct, Podocarpus vitiensis would appear to be derived from 
the P. macrophylliis type of leaf, by the removal of the two lateral resin 
canals away from the median one. 
In other species of the order a reverse change has occurred : reduction 
of leaf surface. Stages in this reduction we see in Microcachrys , Dacrydium 
cupressinum , D. Franklini , and Phyllocladus , the last being the most 
reduced type of leaf in the order. The juvenile leaves of Dacrydium thus 
approach more nearly the primitive form than those of the adult state, as 
would be expected . 1 It is also interesting that the first leaves of the 
seedling of Phyllocladus are flat green needles, the transition between these 
and the very reduced leaves of the adult state being gradual . 2 
In spite of their characteristic venation, the leaves of Nageia have 
a very similar internal structure to the others. A single resin canal 
underneath the phloem of each vascular bundle, and the development of 
transfusion tissue on either side of the xylem, occur exactly as in the other 
species. There can be no doubt that the Nageia type and the remaining 
types of leaf in the Podocarpeae have had an immediate common origin. 
There are two possible alternatives ; either the parallel-veined type is 
primitive in the order, and the uninerved type has been derived from it by 
reduction, or the Nageia type has originated from the Saxegothaea type in 
response to demands for extra leaf surface, as the type of Podocarpus 
macrophyllus has, only with a different result. 
The evidence in favour of the first hypothesis is practically limited to 
the fact that parallel-veined leaves are common in the Araucarieae, while this 
piece of evidence is strengthened by the growing opinion that the Arauca- 
rieae and Podocarpeae are nearly related groups of Conifers. Moreover, some 
Araucarian leaves with only one vein show evidence of having been reduced 
from a wider parallel-veined leaf . 3 The leaves of Cordaites also are parallel- 
veined, and at present the more general opinion of botanists is that the 
Cordaitales and Coniferales are descended from a common ancestor. 
But this resemblance of the leaves of Agathis to those of Nageia is only 
a superficial one. The internal structure of the leaves of Agathis is quite 
different from that of Nageia , especially as regards the distribution of the 
1 Cf. Goebel (’00, p. 154), who says with regard to the leaves of the Cupressineae, which in 
external characters closely resemble those of Dacrydium , ‘ the juvenile forms of these plants must 
undoubtedly be regarded as more primitive.’ 
2 Geyler (’81), p. 209 ; Coulter and Chamberlain (’10), p. 227, Fig. 256, e,p 
3 Seward and Ford (’06), p. 350. 
