1 86 Le Goc.— Observations on the Centripetal and Centrifuga 
The transverse wound was about 6 cm. from the base ; it had cut through 
some two-thirds or three-quarters of the area of the petiole, thus breaking 
the continuity of most of the foliar bundles. The sections prepared from 
the portions situated below the wound showed no abnormality, except 
a reduction of growth in the inactive and useless bundles as compared with 
their companions which had to carry out the whole work. This result is 
what might be expected in view of the fact that the injury cut off the 
supply of food from the leaflets. But just above the wound a remarkable 
phenomenon was observed. We must remember that at this height and 
even much below the wound the xylem was mainly centripetal xylem, dis- 
connected from the centrifugal xylem. The cambium looked very active ; 
it passed all round the bundle, producing xylem towards the centre and 
phloem on the outside (Fig. 12). There was secondary xylem formed even 
behind the centripetal xylem. Such a bundle is difficult to define ; it looks 
concentric rather than mesarch. As we look further from the wound this 
peculiar structure gradually disappears till we finally reach a normal dis- 
tribution of elements in the bundle, perhaps some 3 cm. from the wound. 
It may be noted that this phenomenon occurred in a great number of the 
severed bundles. In connexion with these a new structure was induced. 
A large bundle built up of stout lignified cells, having much the appearance 
of a transfusion tissue, brought all the severed bundles into communication 
with the unwounded bundles, and allowed a transport of material to and 
from the channels interrupted by the wound, like a short loop-line connecting 
the ends of a section of rails under repair (Fig. 13). 
The longitudinal cut was narrow but long, its distance from the base 
varying between 10 cm. and 20 cm. It was situated near the first leaflet 
and higher in the petiole. The leaf reacted against the injury by repairing 
the damage done and filling up the gap with new tissue, disposed in regular 
rows quite distinct from the rest of the petiole. A large bundle, giving rise 
to this tissue, originated in the internal margin of the wound. Its cells are 
pitted and run somewhat irregularly, showing a tendency to imitate the 
transfusion tracheides met with lower down just above the transverse cut. 
The bundles next to the wound were also considerably affected ; they 
became closed and concentric, showing new regions of growth. This 
influence is less marked further away from the wound. The meaning 
of these traumatic structures is considered later. Bertrand and Renault 
tested the effect of longitudinal wounds, but they considered the results as 
accidental and of no significance. 
Interpretation. 
The disposition of the vascular bundles at the very base of the petiole, 
as we have seen, offers a striking appearance. The various forms (Figs. 1-3) 
they assume are, I believe, of no phylogenetic importance, but serve to 
