90 B exon.— Observations on the Anatomy of 
entering the hypocotyl, rotated and formed two root poles, whilst the 
remaining pair of bundles rotated towards one another at the entrance to 
the hypocotyl, and formed the third pole of the triarch root. Later one 
xylem group disappeared, diarchy obtaining throughout the remainder of 
the seedling. 
The remaining seedlings showed a transitory tetrarch stage at the 
apex of the hypocotyl, this being quickly reduced to triarchy by the fusion 
of two of the xylem groups. Reduction to diarchy ensued in both seedlings, 
this being produced in the one instance by fusion of xylem plates, and in the 
other by the disappearance of a xylem plate. 
Syncotyls. Syncotyly, whilst not so frequent an abnormality as poly- 
cotyly in Centranthus , is not by any means a negligible factor in the 
consideration of the seedling structure. 
One of the seedlings examined may be termed a trisyncotyl, since it 
possessed three cotyledons the laminae of 
which were fused laterally for approximately 
half their length. Two of the cotyledons were 
of normal size, whilst the central one was 
considerably smaller (Fig. 9 ). Each of the 
three vascular bundles rotated on entering the 
hypocotyl, this being followed, however, by 
the speedy disappearance of the small bundle 
and the development of diarch structure. 
Three other seedlings were examined in 
which the two cotyledons present were united 
laterally for a considerable portion of their 
length, so that in one case only a slight notch 
Fig. 9. Syncotylous seedlings. appeared at the apex of the cotyledon. Whilst 
these seedlings present interesting details in 
their anatomy, these are not sufficiently relevant to be discussed here, 
but the seedlings are recorded as further examples of a tendency very 
common in Centranthus— the tendency towards fusion of distinct parts. 
Discussion. 
In the investigation of Cheirantkus Cheiri (9) two modes of cotyledon 
increase were recognized : one type a, in which the two cotyledons were 
produced by the qualitative division of the cotyledon apex, so that the 
vascular strand of each daughter cotyledon formed with its fellow one root 
pole, and the other type /3, in which there was a qualitative division of the 
growing point so that the vascular strand of each daughter cotyledon gave 
rise to a root pole independently. 
It will be obvious that the majority of the Centranikns rnber seedlings 
