SEEDLING STRUCTURE IN THE LEGUMINOSJE. 19 
throughout; this, as well as certain histological features, suggesting a 
connection with the neighbouring tribe Genistem. It may be noticed that 
the two largest seedlings with the broadest cotyledons are diarch, the 
three smallest showing tetrarchy (contrast p. 117, &e.). There can be 
little doubt that the three types constitute a phylogenetic series. 
The level of transition shows a definite relation to the diameter of the 
hypocotyl, A series arranged in order of decreasing diameter is also 
arranged in order of increasing height above the collet at which pith begins 
to appear. The largest seedling, Thermopsis montana, may be said to have an 
intermediate transition ; while in the other species the transition is high. 
(2ЕХІЅТЕ ДЕ, 
The Geniste:z include species with a considerable variety of habit; some 
are trees, others large or small shrubs, sometimes leafless or spiny, others 
thick-stemmed annuals. The prevailing habit is woody, and the seedlings 
are sometimes unusually rigid, 
The seedlings are epigeal. The hypocotyl sometimes extends high above 
the ground, sometimes is short so that the cotyledons are unfolded near 
the surface. The cotyledons are more or less fleshy, in some cases becoming 
leaf-like, in others functioning chiefly as storage organs. In most cases, 
owing to the accumbent position of the radicle in the seed and to the 
pressure of the hilum, the cotyledons are somewhat asymmetrical and 
sometimes have a sinus on one side; the venation is pinnate. There is a 
great variation in size of seedling within the tribe, the variation not being 
correlated with the bulk of the mature plant, though perhaps somewhat 
related to the rate of growth. Laburnum vulgare, a tree, has а hypocotyl 
of about 1; the volume of that of Lupinus mutabilis, a low shrub, and 
about } of that of Lupinus hirsutus, an annual herb. Оп the whole, 
however, the seedlings are fairly small, 1:0 mm. being a usual diameter. 
So far as is known, the root is uniformly diarch throughout the tribe, 
despite the variation in size and mature habit ; the xylem plates are never 
uniseriate, so far as known, usually consisting of two rows of stout-walled 
vessels of rather characteristic appearance. In some cases the two xylem 
plates may become continuous through the centre of the stele at the end of 
the first phase of development (e. g. Cytisus spp.) ; in others they remain 
distinct (e. g. Spartium junceum, Lupinus mutabilis). In many cases the 
xylems are more than biseriate and may be wedge-shaped. The primary 
phloems often, but not always, contain fibres. 
The cotyledon trace almost invariably consists of a pair of more or less 
widely separated collateral bundles with endarch xylem, and a small 
intervening protoxylem group which comes direcily from a root-pole ; this 
last may rarely acquire a tiny phloem bundle immediately outside it, thus 
