ANATOMY AND PHYLOGENETIC POSITION OF BETULACEAE 425 
medullary rays are present which are but one or two, rarely four, cells 
in width, the cells being mostly elongated in the radial direction and 
containing clustered crystals. The vessels have small lumina, are 
arranged in radial rows, bear bordered pits in contact with the ray 
parenchyma and always have scalariform perforations. Wood paren- 
chyma is present and is not usually arranged in the plates so char- 
acteristic of Quercus. The wood prosenchyma or tracheids have wide 
lumina and bordered pits, which are not numerous and whose border 
is distinctly smaller than the pit itself. The above statements apply 
to the members of the Betulae (Alnus and Betula). Among the 
Coryleae (Carpinus, Ostrya and Corylus) there are many features in 
agreement with the Betulae. The medullary rays are small, usually 
being from one to two, or sometimes three, cells in width. The wood 
prosenchyma is characterized by wide lumina and bordered pits; and 
the vessels are always arranged radially with small lumina. However, 
where two vessels join each other, the walls bear densely packed and 
rather large bordered pits, the margin often assuming a hexagonal 
contour. Again, where the vessels come in contact with the ray 
parenchyma, their pits are almost entirely simple. There are spiral 
thickenings in some members. In all investigated species of Carpinus 
and Ostrya the perforations of the vessels are, for the most part, simple 
and elliptical, and the scalariform type is confined largely to the 
primary wood. Corylus, however, does have exclusively the scalari- 
form type. The Coryleae in general have more wood parenchyma 
developed than do the Betulae and it is often found in bands as is 
characteristic of Quercus. 
The preceding paragraph will afford an idea of the main features 
of the Betulaceae from the standpoint of wood structure. It is chiefly 
from the evolutionary aspect that they will be treated in this work. 
From this point of view, as in the case of the oaks, the rays show very 
interesting and important conditions. 
Alnus, a genus ranging in stature from the arboreal to the fruticose, 
is generally distributed throughout the north temperate zone, and is 
abundant in eastern North America and in eastern Asia. Its rays 
vary much in size and degree of development according to the species. 
Bailey (1912) has already shown this in some detail. So far as his 
work goes, it has been possible to verify his results. Certain forms, 
as Alnus acuminata, show practically no tendency towards aggregation 
of the ray. Instead, the rays, even in the mature stem, are usually 
