85 
Teratological Seedlings . II. 
another and formed one pole of the diarch root. One of these seedlings 
showed two epicotyledonary leaves, whilst the other showed a whorl of 
three members. 
In the majority of the seedlings the vascular bundle forming the midrib 
of each cotyledon commenced to rotate in the base of the cotyledon petiole 
or at the apex of the hypocotyl, a triarch stage being established, followed 
in most cases by a reduction to diarchy. In about half the seedlings the 
reduction occurred at a fairly high level in the hypocotyl, whilst in other 
cases it was delayed until the lower hall of the hypocotyl or the root was 
Fig. 4. a-e. Ilemitricotyl in which the bundle supplying one lobe of the abnormal cotyledon 
retains its collateral structure. Diagrams b and c show the abnormal bundle with its endarch 
protoxylem, fx. In c the phloem of the abnormal bundle has fused with the half-phloem groups 
on either side to form one long band,/^. Diagram d show? stage at which the metaxylem only of 
the bundle is present. 
reached. Finally, in a few seedlings triarchy persisted throughout the 
whole seedling, but this condition was far less common than in Cheiranthus , 
where more than half the tricotyls examined showed persistent triarchy. 
The reduction from triarchy to diarchy was accomplished by one of 
two methods, either by the gradual approximation and fusion of two xylem 
arms, this being accompanied by the disappearance of the intervening 
phloem group, or by the disappearance of one of the three xylem arms, 
followed by the fusion of the two phloem groups which lie on either side of 
it. Of the two methods the second was by far the more frequent, reduction 
by fusion of xylem arms being comparatively rare. In one only was there 
a condition intermediate between disappearance and fusion. In this instance 
two of the vascular bundles entered the hypocotyl in close proximity to one 
another and rotated in the usual manner, this being quickly followed by the 
disappearance of the median phloem group and a further approximation of 
