666 Worsdell. — A Study of the Vascular System in 
with the petiolar cylinder. When this has happened the bundles forming 
the ventral half of this cylinder begin to pass across and unite with those 
on the dorsal side ; this, however, is not completely effected until some 
considerable distance down the internode of the stem, and long after all 
trace of the petiole-attachment has vanished. We note the presence in the 
cortex of the stem of a bundle-system consisting of two or three ranks of 
strands (as seen in all species of Magnolia ), some of which are concentric, 
others arc-shaped, others again with inverted orientation. 
Peduncle : In this organ the modifications have not been so great as 
those in the vegetative stem ; there are clearly three ranks of bundles 
forming, within a limited area, a scattered system of strands. A difference 
from what usually obtains in stems is here noted, viz. that the largest 
bundles, which are the latest incoming leaf-traces, are outermost , and the 
smallest innermost, the bundles of the two sizes alternating with each other. 
They are all very narrow in the tangential direction. In the cortex occur 
concentric or partially concentric strands arranged in a single ring ; their 
xylem is internal and the phloem external. In the ground-tissue occur 
sclerotic groups of cells. Between the above-mentioned cortical bundles 
and those of the central cylinder, and apparently linking up into one the 
two otherwise distinct systems, is a ring or rank of arc-shaped collateral 
bundles whose shape is obviously intermediate between that of the bundles 
of the cortical system and that of those of the cylinder. These represent 
the components of the dorsal arc which only at this late stage exhibit the 
completion of the process of union with the ventral strands of the petiolar 
cylinder (Fig. 33, Liriodendron ). 
The other species in which I found medullary bundles in the petiole 
are M. macrophylla , Michn., M. acuminata , L., M. grandiflora , L., M. 
conspicua , Salisb., M. Campbellii , Hook. f. et Thoms., and M. Watsoni , 
Hook. f. ; in the last named, two or three bundles from the dorsal side of 
the cylinder seem to make a half-hearted attempt to become medullary, but 
they scarcely leave the cylinder, although they are situated further towards 
the ventral side than are the other larger bundles of the cylinder. 
In Talatima Hodgsoni Hook. f. the medullary bundles, which have a 
very V-shaped xylem, appear in the swollen petiolar base ; they emerge from 
the cylinder on its dorsal side and re-enter it in the extreme base of the 
organ on its ventral side. The ventral bundles here fuse up together to 
form two or three large bundles which, revolving on their axes, enter the 
stem-cylinder independently. 
In Liriodendron one bundle of the cylinder of the petiole tends to become 
medullary ; at the extreme base the ventral bundles anastomose with the 
dorsal, the lateral bundles (about two on each side) remaining free and 
unchanged. There is no persistent cortical leaf-trace system as in Magnolia, 
the change from leaf- to stem-structure taking place more rapidly. 
