4i8 
CARL S. HOAR 
from the Betulaceae and other amentiferous plants. As will be noted, 
the work in this case, as well as in the case of the Gnetales, has been 
for the most part confined to the reproductive structures with no special 
reference to the vegetative bodies. Let us now turn to a somewhat 
brief survey of the latter structures in Casuarina. As work is now 
being carried on in this laboratory with regard to the above, it is not 
necessary to enter into a detailed discussion, but several points may 
be emphasized. 
In studying the anatomy of a group of plants in order to determine 
their evolutionary relationships it is especially desirable to know and 
to be able to interpret their wood structure. Recent work on the 
Gymnosperms has proved of great assistance and one is now able to 
classify them more nearly in a true phylogenetic order. Little work 
has as yet been done upon the Angiosperms; but if the principles used 
in the case of the Gymnosperms are valid, they should hold equally 
in the case of the Angiosperms. 
With this in mind we may turn to the anatomy of the Verticillatae. 
The wood, here, contains vessels which are small in diameter. These 
have, even when in contact with the wood parenchyma, bordered 
pits. Their end walls may often have simple, elliptical perforations 
such as are characteristic of the more highly developed Angiosperms, 
but these, in every case examined, are accompanied by the scalariform 
type characteristic of the lower forms. In some species the vessels 
also have spiral tertiary thickenings. Wood parenchyma is quite 
abundant and is always found scattered throughout the entire annual 
ring in the same position (diffuse) as it occurs in the higher Gymno- 
sperms. With regard to the wood prosenchyma the walls are usually 
thick and possess the bordered pits characteristic of Gymnosperms. 
It is in connection with the rays that the most interesting condition 
is found. Among the Coniferales the rays are uniseriate except in 
the case of those which contain horizontal resin canals. This condition 
is not prevalent among the Dicotyledons, or even among the Gnetales, 
although some uniseriate rays are present. Later it is my purpose to 
trace the evolutionary development of the higher types of rays but 
it will now be advantageous simply to state the situation as it exists 
in the Casuarinaceae. Certain species, such as Casuarina torulosa 
(figure 2), show around the leaf- trace a congestion and grouping of 
the rays into a large, "false ray," — the aggregate type. This character 
persists throughout the entire growth of the plant. In other forms a 
