8oo 
Compton Anatomical Study of 
triad and two edge-veins, each derived from half one of the intercotyledonary 
root-poles. Syncotyly results in a reduction to triarchy and the elimination 
of one of the lateral cotyledon traces, just as in Helianthus. 
General Remarks on Syncotyly. 
A great number of dicotylous seedlings normally exhibit a small degree 
of syncotyly. This is a common occurrence in the Papilionatae, where the 
cotyledons are frequently united for a millimetre or two along the straighter 
edges — i. e. the edges against the accumbent radicle in the seed and opposite 
the first leaf (when unpaired). It is noteworthy that in many such cases 
among the Leguminosae the seedlings are triarch, and the vascular system 
is thus roughly similar in plan to that of a moderately syncotylous Helianthtis 
such as Seedling B . 1 In the syncotyl of Swainsona Cadelli , indeed, we have 
a normally triarch structure remaining practically unaltered by the fusion. 
But we can hardly attribute triarchy to syncotyly in the Leguminosae, for 
the real problem in the case of small triarch seedlings is not the dis- 
appearance of one intercotyledonary bundle but the retention of the other ; 
and this, as I have endeavoured to show elsewhere, is related to the useful 
supplementary function performed by the retained bundle in relation to the 
first primordial leaf . 2 
The chief interest of syncotyly is in relation to the vexed question of 
the origin of Monocotyledons. It is widely admitted that the forms with 
one seed-leaf have been derived from ancestors with two, and the problem 
is the method or methods by which this reduction in number has occurred. 
The two possible methods by which one seed-leaf may be derived from two 
are (i) by lateral fusion or syncotyly ; (2) by the elimination or change in 
function of one cotyledon, or heterocotyly. Both these methods have been 
supposed to have taken place in various instances, and the rival schools, 
assuming monophylesis of the Monocotyledons, have warmly debated the 
alternatives. One of the most recent presentments of the problem, however, 
is that of Lotsy , 3 who considers that the Monocotyledons are at least 
diphyletic, and that both methods may have been adopted in different 
groups. Lotsy considers that the syncotylous origin of monocotyly is less 
well established than the heterocotylous, but that the former view derives 
support from the occurrence of syncotyly among undoubted Dicotyledons. 
He, indeed, regards the theory that the epiblast and the scutellum in the 
Gramineae are respectively equivalent to reduced and suctorial cotyledons 
as better supported than the syncotylous theory of the origin of mono- 
cotyledony. Here the present writer cannot follow Lotsy, having regard to 
the great diversity of opinion which still exists as to the morphology of the 
Grass embryo. But leaving this point on one side, if we accept the view 
1 Compton (’12 b ). 2 Compton (’12 b ), p. ioi. 3 Lotsy (’ll), p. 624 . 
