SEEDLING STRUCTURE IN THE LEGUMINOSAE. 39 
relatively to the xylem at the node. As we ascend into the cotyledonary 
lamina, however, the xylem gradually becomes mesarch and then endarch, 
and the phloems slowly move to the dorsal position. 
(ii.) In the triarch type (fig. 87) the three-rayed xylem star persists until 
nearly half-way up the hypocotyl. Then, as the pith begins to appear, two 
xylems (the polar ones) gradually inerease their angular distance until they 
become opposite ; the phloem between them divides into two parts, and the 
metaxylem on the side of the pith opposite to the third xylem acquires a few 
protoxylem elements (fig. 88). Thus a tetrarch arrangement is produced, 
and, by the equalisation of the lateral groups of xylem, the structure assumes 
the same symmetry as is found in seedlings with tetrarch roots (fig. 89, 
taken from a triarch seedling). 
(11.) The diareh type is a further simplification, and passes into the tetrarch 
symmetry in the course of the hypocotyl in a mode similar to that pursued in 
the transformation from triarch into tetrarch. It may be noted that the two 
missing lateral groups of xylem do not appear simultaneously, but that as we 
pass up the hypocotyl we find a triarch stage intervening between the diarch 
and the tetrarch. 
Measurements reveal no differences in size between seedlings showing 
different types of symmetry (cf. Caragana arborescens). 
GALEGEZE. 
INDIGOFERA GALEGOIDES, DC. 
Tall shrub. Hypocoty] tapering slowly into the long primary root. Cotyle- 
dons ovate-oblong. The hypocotyl is somewhat downy. 
The root is tetrarch, the xylem being in a solid four-rayed star 6 mm. 
below the collet. Here the changes begin ; a pith appears, and the xylem is 
speedily broken up into four solid equilateral wedges. Fibres and tannin- 
sacs are present in the phloem. At the collet the four xylems are contiguous, 
but higher up they separate completely and each becomes radially crushed 
into a tangential position: the protoxylems projecting outwards slightly. 
2 mm. below the cotyledons the lateral xylems divide and the halves go to 
join the polar groups ; a double bundle is thus formed at each pole of the 
ellipse, but each of the two bundles composing it is clearly made up of polar 
and lateral groups. At the departure of the cotyledon the double bundle is 
practically endarch ; and the transition is completed in the region of 
branching by fusion in the median plane. 
INDIGOFERA TINCTORIA, Linn. 
Hypocotyl hairy. Cotyledons ovate. De Candolle (1825, pl. 7) gives a 
figure of a seedling. 
Seedlings supplied under the name J. sumatrana, Geertn., agreed closely 
