SEEDLING STRUCTURE IN THE LEGUMINOSJE. 31 
xylem vessels have lost the stoutness and coherence they possessed below). 
At 1 mm. below the node the xylems are Y-shaped, and become T-shaped on 
entering the cotyledons. The transition is therefore high ; and the structure 
exhibits some relationship to that of both Trifolieæ and Geniste, with the 
additional feature of the reduction from tetrarchy to diarchy (cf. certain 
Podalyriez). Two other seedlings exhibited an essentially similar structure. 
In a seedling with three root xylems it was found that at the collet region 
two of the xylems increased their angular distance and the intervening phloem 
divided ; simultaneously, a fourth group of xylem appeared in the gap thus 
produced, and increased in size until the structure became symmetrically 
tetrarch. The new group of xylem was completely detached from the others. 
Higher up the hypocotyl the two intercotyledonary xylems disappeared as in 
the first instance, leaving the xylem system diarch. The new xylem is one 
of those to disappear, so that it has a relatively short and completely 
independent course in the hypocotyl. 
Two other seedlings also showed triarch roots. In one case the passage to 
tetrarchy was effected 5 mm. below the collet. In the other a vestige of a 
fourth xylem appeared half-way up the hypocotyl, when the other inter- 
cotyledonary xylem was already dwindling ; the change to diarchy was 
made as usual, so that in this case the fourth xylem was a mere vestige only 
about З mm. in length. Such a bundle, confined to the region between half 
and three-quarters of the way up the hypocotyl, could hardly have much 
functional significance. 
MEDICAGO TRIBULOIDES, Desr. 
A sprawling annual herb. Cotyledons green and leaf-like, slightly turned 
to one side, the edges on one side being straight, on the other curved. 
The root is tetrarch, the xylem consisting of four 1-2-seriate plates of 
spiral and pitted vessels, which meet in the centre of the stele. Each of the 
four phloems contains a group of strong fibres, which is bounded externally 
by the 2-3-layered pericycle, internally and laterally by an are of thin-walled 
phloem. The endodermis is sharply marked with dots on the radial walls. 
This configuration of the xylem persists for about two-thirds of the way up 
the hypocotyl without undergoing any change except the disorganisation of 
the spiral protoxylems. | Each phloem, however, suffers a change, and comes 
to consist of a group of large clear cells with hardened but scarcely thickened 
walls flanked by a group of sieve-tubes and eompanion-cells on either side, 
The impression is given that the phloem has divided into two groups 
separated by conjunctive parenchyma ; but this is illusory: a little typical 
phloem-tissue oceurs in a narrow band inside this clear-celled group, which 
should be regarded as the representative in the hypocotyl of the fibres in the 
root. The endodermal dots disappear also in the lower part of the hypocotyl. 
The transitional changes of configuration begin about two-thirds of the 
