104 MR. R. H. COMPTON: AN INVESTIGATION OF THE 
Further, it may be observed that in those triarch cases where the 
cotyledons are markedly asymmetrical (p. 77) the third root xylem is on 
the side of the narrower halves of the cotyledons, which thus receive the 
greater vascular supply. In fact it appears that triarchy exists in spite of 
the asymmetry of the cotyledons and not in connection therewith. 
We may therefore conclude with some certainty that in slender epigeal 
seedlings the lateral root-poles, when developed, stand in a far more intimate 
relation to the plumular traces than they do to the cotyledons ; and, further, 
that this relation is not complementary but supplementary. 
We must therefore distinguish between the two different róles which the 
intercotyledonary primary xylems of the hypocotyl play in relation to the 
plumule. They may either (i.) form a continuous primary connection from 
root to leaf without relation to the cotyledons ; or (ii.) they may be part of 
the cotyledonary vascular system, but have a more intimate supplementary 
physiological relation with the plumular traces. 
The intercotyledonary xylems may also play another part, which will be 
diseussed in the next section. 
TETRARCHY. 
In many cases of tetrarchy in slender epigeal seedlings of the tribes 
Trifoliee, Lotez, Galegeæ, and Hedysares, we have seen that the lateral 
root-poles in function mainly supplement the earliest plumular traces. In 
some cases (e. g. Melilotus arvensis, Chorizema cordatum) it has been shown 
that the lateral xylems never enter the cotyledons, but die out in the upper 
part of the hypocotyl. "We therefore enquire the reason why, in the majority 
of instances, the lateral xylems though plumular in function yet pass into 
the cotyledons. 
In large epigeal seedlings it has been repeatedly shown that the lateral 
xylems of the tetrarch root bifurcate on passing up the hypocotyl, half of 
each passing out, without noteworthy reduetion in importance, to each 
cotyledon, where (often after a brief fusion with the products of the polar 
xylems) they become the lateral bundles of the lamina. In these cases the 
intercotyledonary xylems play an important part in the vascular system of 
the seedling ; and whether they later enter into relations with the epicotyl 
or not, their primary function is to supply the cotyledons. The greater bulk 
of these seedlings demands a more complex vascular system than is afforded 
by the polar root xylems, though the latter are adequate in many slender 
seedlings *. 
* Out of the 28 epigeal species of Leguminosz the diameter of whose epicotyl is 2:0 mm. 
or more at the base, and 1:5 mm. or more at the summit, 25 exhibited, at least at some level 
or in some specimens, a tetrarch symmetry. The exceptions were two species of Genisteze 
with diarch, and Erythrina indica with heptarch structure. 
