668 Proceedings of Royal Society of Edinburgh, [sess. 
the dependence of the stele on the close lateral approximation of the 
bundles for continuity of the tissues of external conjunctive, since 
the latter are primarily arranged in relation to the separate bundles. 
Flot has not recognised with sufficient explicitness the ex- 
istence of cases such as this. 
The ‘ rays ’ do not exist here as parts of the external con- 
junctive, nor is there a continuous perimedullary zone. We have 
simply a small celled investment of each bundle, on the outer side 
forming a broad band, and giving rise to masses of fibres (the 
“fascicular pericycle ”), and internal to the apex of the proto- 
xylem consisting of a considerable mass of parenchyma, while 
on the flanks of the bundle it is two or three layers only. This 
tissue is continuous from bundle to bundle by the single layer of 
small cells above described (the “interfascicular pericycle ”). This 
disposition is common enough in hypocotyls, where the bundles are 
widely separated. The individuality of the bundle as a unit of 
vascular tissue here comes out very markedly. It is the bundle 
which is surrounded by small celled tissue. The continuous 
parenchymatous pericycle of the root is still present at the base 
of the hypocotyl, hut soon loses its continuity across the phloem as 
we pass upwards, and is interrupted by the masses of fibres 
abutting on the endodermis and developed very obviously from 
the same mass of procambial tissue as the phloem, as can be well 
seen in the embryo and very young seedling. About the same 
level the cells of the endodermis lose their characteristic thicken- 
ings, and are sometimes only distinguishable from the adjacent 
cortex by the possession of starch — a character which is itself lost 
later on. The object of the starch in the endodermis is obviously 
to supply the pericyclic fibres with material for thickening their 
walls, and in the portions between the bundles to feed the inter- 
fascicular cambium. As these two processes proceed it gradually 
disappears. The interfascicular pericycle itself is simply the birth- 
place of the interfascicular cambium, the cortex dipping between 
the bundles just far enough to bring the pericycle opposite the 
bands of small celled tissue between the xylem and phloem in 
which the fascicular cambium arises. Thus we may almost say 
that the stele of the root is preserved in the hypocotyl only as 
a matter of convenience ; the bundle is the important unit.. 
