460 Harvey -Gib son. — Contributions to Knowledge of 
steles of the main axis. The aerial and subterranean parts of 
the roots both contain normal-monarch cords. Root-hairs 
are abundant. .S', rubella , Moore, agrees in all essential 
respects with 6'. Galeottei. 
In S. Kraussiana , A. Br., the roots arise singly at each 
forking of the stem on the upper side and arch over to the 
side of the stronger branch. Since the branches are alternately 
right and left, the roots are alternately left and right. Each 
is unbranched until it reaches the soil and then it branches 
profusely. Anatomically the vascular cylinder of the aerial 
part arises from the vascular system of the stem at the junction 
of the stem-cords. The aerial portion, as has been already 
pointed out by several authors, is centroxylic (PI. XX, Fig. 17), 
and remains so until the subterranean parts are reached when 
the root becomes normally monarch. X. Kraussiana has 
hitherto been regarded as the solitary exception in this 
respect. X. Poulteri , Veitch, and S. delicatissima, , A. Br., 
however, show precisely the same centroxylic condition in the 
aerial roots, like X. Kraussiana becoming monarch in the 
subterranean portions. 
Turning now to the species usually designated as tristelic, 
it may be said that they agree in almost all respects with the 
majority of the species already described in the monarch 
character of their root-cylinders. 
The root of X. canalicidata , Bak., in its aerial part shows 
a slightly crescentic xylem and a protoxylem situated in the 
middle of the crescent. The mode of origin of the steles of 
the root is as follows : — From the upper and lower steles of the 
stem vascular strands are isolated (PI. XXI, Fig. 24, 1), then 
one from the middle strand, and at the same time one for 
the ventral leaf (2) ; the middle stele then broadens and forks 
and a strand is given off the lower stele (3) ; the upper stele 
then bends down and unites with the upper branch of the 
fork of the middle stele, the lower branch uniting with the 
offset of the lower stele (4). The middle stele is now isolated 
and the fork portion is still united with the upper stele (5) ; 
the three steles of the lateral branch are thus distinct. The 
