TO Brrp’s-EYE FORMATION IN THE WOOD OF TREES. 23 
cambium, and phloem of the stem is quite evident. A series of 
transverse sections showed that those papilla were undoubtedly 
the beginnings of adventitious roots which spring from rhizo- 
genous medullary rays. Their passage through the wood and 
bast presents the same features as those already seen in Lawson’s 
cypress. In the wood-portion the characteristic incurving of 
the tracheids was very marked. The cortical cells to the side 
of the protruding cone (see Plate VIII., Fig. 13) are stretched and 
elongated, while those in front are crushed and flattened. There 
is also a striking difference between the size of the cells in cone 
and cortex. The appearance of a transverse section through 
the middle of one of these adventitious roots of Thuja gigantea is 
shown in Plate VIIL., Fig. 10. The axile portion is surrounded by 
an endodermis outside of which lies the relatively broad cortex. 
The vascular bundle is tetrarch, being composed of four patches 
of primary xylem between which are placed the phloem-bundles. 
An enlarged view of the central portion of this root may be seen 
in Plate VIII., Fig. 9, where the structure can be made out better. 
A section through the tip of this root merely showed an 
undifferentiated mass of small-celled parenchyma-tissue. 
Maple. 
Three young maple-trees growing in the Botanic Garden 
exhibit a similar phenomenon. They occur in the midst ofa 
clump of other trees and shrubs of various kinds. The soil in 
which they grow is well supplied with water, and the shade 
and shelter afforded by the other trees keep the lower portion of 
their trunks fairly moist. Their ages, as ascertained by 
Pressler’s increment-borer, vary from 12 to 15 years. The only 
one which was sufficiently isolated to photograph is shown in 
Plate IX., Fig. 14. This photograph was taken about the 
beginning of April. The foliage-buds were then well advanced, 
and a fortnight later the lower part of the tree was covered with 
leaves, which, however, subsequently suffered severely from late 
frost. Plate IX., Fig. 15, is a nearer view of the limb of this tree 
to the right, just where it makes a bend to the left, and on it may 
be seen an abundant development of conical protuberances. 
Plate IX., Figs. 16 and 17, are portions of the other two trees, 
