476 DR. ERIC DRABBLE ON THE 
inrolled that a complete ring of tissue is formed in which the xylem- and phloem-groups 
are only wanting for a short space internally. Round these the endodermis is nearly 
continuous. Through each gap the parenchymatous tissue of cortex and medulla is 
continuous, and fibrous bundles are very abundantly developed in the medullary 
portion. 
(e) In sections from a still more proximal portion of the same root the vascular 
cylinder consists of a greater number of separate ares, many of which form nearly 
complete cylinders. The xylem-groups of the internal portion of these cylinders are 
approximated by their protoxylem-elements, the metaxylem portions divaricating widely. 
A phloem-group occupies the innermost point of such a cylinder (text-fig. 17). Such a 
complete ring of fibrous tissue encloses a portion of the general parenchymatous ground- 
tissue, continuous below with the medulla, when the ring becomes incomplete internally. 
In this central parenchyma occur two or more strands of fibres similar to those of the pith 
and cortex. 
The endodermis is in this region strongly lignified on all but the external tangential 
walls, and here and there occurs a non-lignified passage-cell. When present, such a 
cell usually occurs opposite to a protoxylem-group, but they are rarely developed, 
the endodermal cells opposite the protoxylem being generally quite as densely lignified 
and thickened as elsewhere. Not infrequently the endodermis is locally doubled ; 
this occurs generally immediately distally to the closure of the gaps in the central 
cylinder. 
Between two inrolled edges of the fibrous zone, just before fusion takes place, the 
parenchymatous cells of the ground-tissue are often greatly crushed, and their lumina 
may even be entirely obliterated, showing that a differential rate of expansion has taken 
place since the procambial tissue was laid down in the apex. 
Similar crushing may also occur between the nearly fused internal edges of greatly 
inrolled arcs of the fibrous zone. Some of the segments of the central cylinder are 
very small and may contain as few as one xylem- and two phloem-groups, the endodermis 
only bounding the peripheral surface. Others contain three xylem- and five phloem- 
groups; others are more extensively provided with endodermis investment. In the 
medullary tissue run isolated strands of fibrous tissue, many of which possess a xylem- 
group consisting of one large vessel and two or three smaller ones. In other cases only 
the large vessel is present. In one case an interesting condition was observed in the 
presence of a phloem-group, quite unaccompanied by xylem, running just internally to a 
gap in the fibrous zone. Occasionally a medullary fibrous strand may enclose a central 
large vessel from which protoxylem-groups to the number of 3-5 radiate, alternating 
with which two or more phloem-groups occur. 
At some gaps in the fibrous zone, even when the endodermis is complete across the 
= SE ue SOM TEST ` KEE EE : 
SE We EE SC e 
