674 
PROFESSOR F. 0. BOWER ON THE DEVELOPMENT AND 
cellular spaces, the cells being rounded, with thin walls, and containing protoplasm 
with chlorophyll granules. Here again there is no clear limit between the outer tissue 
and the vascular tissue; on passing from the periphery inwards the intercellular 
spaces become smaller, and in the tissues immediately surrounding the xylem they are 
almost or entirely absent (fig. 39); there are, however, intercellular spaces between 
the elements of the xylem themselves. The thin-walled tissues surrounding the 
xylem show characters similar to those of the tissue in a similar position in the leaf, 
which suggest for them a similar function. The elements of the xylem are tracheides 
with annular or irregular spiral and reticulated thickening of the walls. 
A transverse section of a mature root shows a structure which coincides with that 
of the simpler forms of root in the Lycopodince. There is no clearly defined epidermis; 
cells of the superficial layer grow out as simple root hairs. There is a broad band of 
cortex with large intercellular spaces ; it is limited internally by the bundle-sheath, 
which is not a definite layer of cells, but is, as in Lycopodium, a somewhat irregular 
band of cells with corky walls (fig. 41) ; between this and the vascular tissues an 
irregular band of cells with cellulose walls intervenes, which may represent the 
pericambium. The vascular tissues consist of a single group of xylem elements, and 
a single group of elements of the phloem. No example of branching of the root has 
been observed. 
As regards the distribution of the vascular bundles in the whole plant, and their 
mutual relations, there is considerable irregularity; this might be anticipated from 
the irregularity of number and arrangement of the leaves, &c., as above described. 
From each leaf one bundle of the leaf-trace passes into the axis ; one strand passes 
from the axis into each root, and, as above described, one vascular strand passes into 
the stalk of the tuber. These are the fundamental points on which the arrangement 
of the vascular tissues is based. Taking first the simple case where only vegetative 
organs are formed, the vascular system was found, in tw r o specimens, each with four 
leaves and one root, to be disposed as shown in fig. 42a. The bundles from three of 
the leaves united in the axis to form one trunk, which was continuous downwards 
directly into the single root. The bundle from the fourth leaf, probably the latest 
formed or supernumerary leaf, was traced directly downwards into the stalk of the 
tuber, without its being connected with the other bundles. This arrangement is a 
very simple one, and is obviously less efficient than those to be described below, since 
the vascular system here consists of two disconnected portions. In another specimen 
having five leaves, two roots and a new tuber, the vascular system was found to be 
disposed as shown in fig. 42 b. The bundle passing down from one leaf, obviously 
from its position the first formed leaf of the successive whorl, divided in the axis into 
three strands; of these one passed to the stalk of the tuber ( t ), the other two curved 
to right and left, and finally coalesced with those descending from the other leaves, to 
form two trunks which passed directly into the two roots (r). 
In those plants which bear sporangia, seated on an elongated stalk or peduncle, a 
