1898 - 99 .] Edith Chick on Bicinus Communis. 
667 
separated by narrow rays five or six cells broad (fig. 30). Those 
which will go off to the first pair of leaves are the oldest and most 
fully developed, while those passing downwards from the youngest 
leaves are only represented by a mass of procambial tissue, which 
will become phloem, the xylem vessels being indistinguishable 
so far from the node at which the development of the traces 
in question begins. The bundles are often so close together 
that the arcs of pericyclic fibres belonging to each coalesce, 
forming an almost continuous ring of fibres, only broken where 
there is a wider gap between two adjacent bundles. The most 
fully developed bundles have an arc of fibres three or four layers 
thick lying outside their phloem, while for the most part a single 
layer only is found outside the younger bundles. The fibres are 
never found except in connection with the phloem. If the bundle 
is so young as to have no xylem distinguishable, and only small 
cells to represent the future phloem, to the outside of this rudi- 
mentary bundle, fibres, or cells already having the form of fibres, 
though unthickened, will be found; but in the gaps between 
bundles an inner layer of cortex, which can often be distinguished 
as a starch sheath, bends down a little, and comes to lie on paren- 
chymatous pericycle cells. But the distinction between the cortex 
and pericycle, when the latter is parenchymatous, cannot always be 
made. 
A further result of the close juxtaposition of the bundles is to 
bring the small cells which cover their flanks into contact, so 
that we get rays of small celled tissue formed (in the outer parts 
of which the interfascicular cambium arises), and even sometimes 
a continuous perimedullary zone, the pith being, as it were, pushed 
back by the closing up of the bundles (fig. 30). (At a a small 
celled ray is partially formed, a large pith cell occupying the 
position midway between the protoxylems, owing to the sloping 
away of the small celled tissue on the flanks of the adjacent 
bundles.) 
These relations illustrate (1) the primary importance of the 
bundle as an anatomical unit in the stem of typical angiosperms, 
— an importance which has, of course, been recognised ever since 
modern plant anatomy had an existence, but has perhaps been 
somewhat obscured of late by the stelar point of view ; and (2) 
