24 BORTHWICK—ADVENTITIOUS ROOTS AND RELATION 
while Plate IX., Figs. 18 and 19, are nearer views of parts of Plate 
IX., Fig. 17. | It will be seen from the figures that the protuber- 
ances occur irregularly distributed over the surface of the stem and 
have no definite sequence of development and also that they may 
occur singly or in dense clusters. Many of the outgrowths on the 
trees shown in Plate IX., Figs. 14 and 17, have pierced the peri- 
derm and protrude as short, white cylinders; whereas, on the 
specimen in Plate IX., Fig. 16, the periderm has merely been 
raised into papilla but has not yet been pierced. Those endo- 
genetic structures do not necessarily make their appearance 
externally, even as minute papillze on the periderm, till some time 
after their formation. | When visible from the outside they can 
be traced back through two or three or more year-rings of the 
wood. In fact a tangential longitudinal section of the stem at 
one of those root-clusters shows all the appearance of the so-called 
Bird’s-eye Maple. In Plate IX., Fig. 19, the lower part of 
a root-cluster has been cut away in order to show this feature. 
The specimens shown in Plate IX., Figs. 20, 21, and 22, are 
instructive and illustrate several important features. The top 
specimen in Plate IX., Fig. 21, is a short cylinder extracted by 
means of Pressler’s increment-borer, and has one of these conical 
projections at its apex. The lower specimen of the same figure 
proves that the core of the cone is in organic connection with the 
wood-body of the stem, the cap-like covering of the bark having 
been lifted off. An enlargement of this specimen is given in Plate 
. Fig. 22, in order to show that the woody-cone does not 
eerie in a single point, but runs out into several fine threads. 
In the cap-like portion at the top of this figure the outer cork 
layers are seen to have been ruptured by the emergence of a 
whitish cylindrical protrusion. The bottom specimen of Plate 
IX., Fig. 20, is a cylinder split longitudinally. The darker central 
band is the basal continuation of the protuberance through the 
wood-body of the stem. The middle specimen is a cylinder in 
transverse section and shows two such round swollen rhizogenous 
medullary rays on their passage through the wood ; while at the 
top of the same figure is a part cut out of a stem ‘wih scarcely 
any apical papilla, although a dark streak may be detected 
running in towards the pith. This is the commencement of one 
of these outgrowths. Plate IX., Fig. 25, shows, greatly enlarged, 
