522 
Holden and 3 exon.—Observations on the 
which persists until a later stage, thus resembling the condition of affairs 
characterizing Phacelia tanacetifolia as reported by Compton ( 4 ). 
In one case a seedling, which had shown reduction from tetrarchy to 
triarchy by the disappearance of a xylem plate, showed a further reduction 
to diarchy in the root, this being accomplished by the fusion of the xylem 
masses and the obliteration of the phloem group lying between them 
(Fig. 17). 
One other type remains to be described in which two of the cotyledons 
had double bundles, whilst the other two showed collateral bundles which 
in the transition region behaved as the constituent halves of a double 
Fig. 17. a-f Tetracotyl showing reduction from tetrarchy to triarchy by loss of one xylem 
pole, and from triarchy to diarchy at a later stage by fusion. 
bundle. Triarchy is thus immediately established and persists throughout 
the seedling, although there are signs of incipient diarchy near the apex of 
the root, one phloem being very much reduced, whilst the poles on either 
side are quite near to one another. 
The epicotyledonary leaves appear to be three in number in most 
cases, but in one there are four leaves, and a further example shows the 
interesting condition in which two normal leaves and one exhibiting partial 
fission are evident (Fig. 15,#, b). 
It will thus be perceived that in the assumption of tetrarch symmetry 
there is a distinct tendency on the part of the first epicotyledonary leaves to 
