358 MISS M. G. SYKES ON THE SEEDLING AND 
throughout the parenchyma (Pl. 35. fig. 19); and as the termination of the bundles is 
approached, this transfusion-tissue increases in amount. The bundles have kept pace 
with the upward growth of the ridge: in the upper and now free and elevated portion of 
the ridge the bundles of the outer series run inwards and terminate together with the inner 
series in a common irregular mass of scattered transfusion tracheids (Tr, Pl. 35. fig. 16). 
Anastomoses are frequent, so that the ridge is provided with a peripheral network of 
bundles running a little way beneath its surface. This is incomplete and open below, 
where the bundles run down into the hypocotyl and there join the main stele of the 
seedling, At this stage free endings are rare, most of the bundles having now become 
joined up with the four groups of vascular tissue found traversing the hypocotyl. The 
bundles of the ridge join on to the same two groups which supply the bundles of the 
subtending leaf. 
(c) In the later stages (e. g., Pl. 34. fig. 4) no important change takes place in the 
structure of the outer ridge. A large number of new bundles are intercalated by the 
rapid meristematic divisions of the parenchymatous tissue; these are chiefly added to 
the outer series, where they are often arranged in two or more rows, all with the xylem 
on the inner side of the bundle *. 
In many cases the first-formed elements of the xylem in these additional bundles are 
not the innermost ones ; but while a large portion of the later-formed xylem is centri- 
fugally developed, a few tracheids are produced centripetally. Sometimes the centri- 
petally developed xylem even exceeds the centrifugal in amount (Pl. 35. fig. 20). Nearly 
all the bundles are accompanied on the centripetal side by transfusion elements. 
There is an inereased number of small transverse bundles at this stage, connecting the 
two series in the outer ridge. 
The inner ridge is now traversed by a number of bundles (Pl. 35. fig. 18), most of 
which are connected with the inner series of bundles belonging to the outer ridge. In 
many cases they can be seen originating from this inner series and running in between 
the leaf-bundles at the base of the leaf-groove ; they then bend upwards and form the 
irregular series of bundles which traverses the inner ridge and surrounds the cotyledonary 
buds: like the bundles in the outer ridge, they end in groups of transfusion-tissue. 
Finally, in the oldest plant examined (Pl. 34. fig. 7) the following was the course of 
events as seen in a series of transverse sections :—In the uppermost portion of the outer 
ridge there is no sign of vascular bundles; about a centimetre from the surface are à 
number of groups of transfusion-tissue, which represent the endings of vascular bundles. 
These vascular bundles are mostly horizontal and are all very irregularly distributed, 
but followed downwards they are seen to become separated into two series orientated 
inversely to one another, between which run transversely a number of connecting 
bundles. Lower down these cross-connections decrease in number. At each end of the 
ridge a bundle, which represents one of the pair of bundles formerly passing out into à 
cotyledon, is still conspicuous and now functions as part of the vascular supply to the 
P At the base of the outer ridge the inner series is much distorted, and its bundles 
twist round and anastomose with one another. Some of them join on to the outer series 
* Cf. concentric rings in Cycads ; also cf. trunk of Cycadella, Wieland, p. 66, fig. 35. 
