400 BOTANICAL GAZETTE [ DECEMBER 
(3) The internal phloem may form an entire cylinder. 
(4) Where gaps are complete, the cortical and medullary 
tissues connect through them. 
(5) Thus sclerenchyma of the cortex is sometimes continu- 
ous with sclerenchyma in the medulla of the main axis, and of 
the branches. 
(6) O. cinnamomea presents the following forms of ramular 
gaps arranged in order of degeneration, (2) complete gaps, (4), 
phloem and xylem only open, (c) the xylem alone opens, (@) 
no gaps at all. 
(7) O. regalis and T. barbara show gaps in the xylem only, 
and in O. Claytoniana there are usually none at all. 0. Claytont- 
ana, therefore, presents the extreme case of degeneration. 
THE. LEAF TRACE. 
The leaf traces pass very obliquely up through the external 
cortex. A section of a leaf trace shortly before it passes into 
the petiole presents some noteworthy characters. In the first 
place there is no pith, but a solid horseshoe-shaped mass of 
xylem with the convex side turned outwards (jig. 5, *). The 
xylem is made up of large scalariform tracheids with a protrud- 
ing mass of a few small vessels constituting the protoxylem. 
The protoxylem is situated on the inner face of the single strand 
of xylem (fx), and is continuous with that of the stem. In Z. 
barbara it frequently breaks into two or three groups. 
Surrounding the wood is a layer of parenchyma, which on 
the concave side of the xylem quite fills the space between the 
arms of the horseshoe. The phloem consists of a crescentic 
band of sieve tubes, one to three cells thick on the external 
side of the leaf trace (p2), and a smaller band on the opposite 
side (gk). The protophloem consists of small elements which 
form a ring, broken only on the concave side of the xylem. 
Here the ring is completed, however, by the inner band of 
metaphloem. In Q. cinnamomea and T. barbara isolated proto- 
phloem cells have been observed by the writer on the side of the 
inner band of metaphloem towards the stem axis. On the convex 
