SEEDLING STRUCTURE IN THE LEGUMINOSA. 47 
tetrarch seedlings ; it is initiated at the collet by the appearance of a pith ; 
the lateral bundles divide about three-quarters of the way up the hypocotyl, 
and fuse with the halves of the polar bundles. At the node each cotyledon 
trace consists of a pair of collateral metaxylem bundles with protoxylem 
between. On entering the cotyledon each of the two bundles forks, the 
adjacent halves fusing together ; and throughout the cotyledon there run a 
median endarch collateral bundle and a pair of lateral bundles. 
Three or four epicotyledonary branches arise at the node, as well as axillary 
buds borne on the short cotyledon tube (compare Coronilla varia, &c.). 
) I , 
SconPIURUS SULCATA, Linn. (РІ. 8. figs. 94, 95.) 
The hypocotyl slowly tapers into the primary root. The cotyledons are 
linear. 
The root is triarch, this arrangement persisting until just beneath the 
external collet. In the upper part of the hypocotyl a tetrarch structure 
obtains; the transition from triarchy to tetrarehy usually occurs at the external 
collet, but occasionally not until half-way up the hypocotyl. 
Just below the collet three equal and equidistant 1—2-seriate xylem plates 
are present, surrounding a fair-sized pith. In the more usual case, the axis 
dilates below the collet, one of the phloems divides, and a fourth xylem, 
unconnected with the others, appears between the two halves (fig. 94). 
This new xylem gradually increases in size, and the axis slowly takes up a 
regular symmetry, all the xylems being equidistant (fig. 95). Sometimes, 
however, the fourth xylem does not appear till half-way up the hypocotyl ; 
and in this case it arises as a branch from one of the other xylem groups. 
The difference in the insertion of the fourth xylem in the two cases would 
seem to be related to its value as a water-channel: in the first case it derives 
its water-current directly from the absorbing surface of the root; in the 
second it is merely an accessory conducting strand. 
Whatever the origin of the fourth xylem, the upper half of the hypocotyl 
has a uniform structure. The polar bundles broaden into a V-shape, re- 
maining exareh. The lateral xylems broaden into the tangential position and 
divide, half of each moving to each pole and fusing with the polar meta- 
xylems. The phloems suffer no change. Thus at each end of the (now 
elliptical) stele there is a double bundle, with three protoxylems, one in the 
middle and one at each extremity, and two phloem groups. Though all the 
xylem fuses together, just below the cotyledonary node the lateral groups 
again become free, so that each cotyledon receives a median double bundle 
of xylem and a pair of lateral groups, the phloems being inserted outside the 
gaps between median and lateral xylems. 
Two or three branches arise at the cotyledonary node without reference to 
the cotyledons, and their internodes are very short, so that a rosette of leaves 
is formed. 
