5°4 
G Wynne- Vaughan. — On some Climbing 
three to five tracheae thick. The flanks are very stout and have quite 
distinct external lateral bays. At some distance from the stem three 
protoxylem groups are present, but these die out before the trace enters the 
cortex of the stem. The protoxylem strands have usually well-marked 
groups of cavity parenchyma in front of them. In weaker petioles the 
xylem of the hooks diminishes till it may be represented by a single series 
of tracheae. 
Within the endodermis of the petiolar trace is a pericycle two or three 
layers thick on the abaxial and concave surfaces, and three to five layers 
thick at the sides opposite the bays. The phloem extends all round, 
but the protophloem is confined to the outer side, being entirely absent in 
Text-fig. 7. Davattia fumarioides. A 1 . Diagrammatic transverse section of petiolar trace at base 
of free petiole, a 2 . Same, some distance up. b. Trace of primary branch at base of the branch. 
C 1-3 . Departure of xylem strand to a secondary branch. D. Primary branch trace above its second 
branch. E 1 * 2 . Traces in secondary and tertiary branches. 
the concavity ; the phloem is in greatest quantity opposite the lateral bays 
and in the bays of the hooks. 
When the trace is closed up and has become reniform in transverse 
section, the middle of the strip of tissue between the halves of the xylem 
strand consists of pericycle which is often somewhat lignified ; this is lined 
on either side by phloem. Farther up, when the xylem masses of the 
flanks begin to approach each other, the pericycle disappears, and the 
centre is occupied by a strip of phloem. Still farther up the phloem 
is reduced to a single row of sieve-tubes separated from the tracheae 
on either side by cells of the xylem sheath. 
The fact that the petiolar trace of Davallia fumarioides appears to be 
more open in the basal region is not surprising. The climbing habit is not 
immediately impressed upon the petiole. At first its structure is like that 
