92 Bexon. — Observations on the Anatomy of 
In the Centranthus seedlings the somewhat smaller size of the collateral 
bundle together with the occasional reduction in size of the cotyledon 
lamina might be adduced in support of the first alternative, namely, that 
the abnormal cotyledon has arisen as a result of lateral fission ; but the 
anatomical structure is difficult to reconcile with such an origin. All three 
cotyledons show the typical arrangement, that is, a median bundle flanked 
by two laterals, these fusing with the central one at the base of the petiole. 
The acceptance of this interpretation would therefore involve the assump- 
tion not only that the ‘ promoted * lateral had undergone downward pro- 
longation into the hypocotyl, but also that new laterals had been developed 
in each of the two cotyledons resulting from the fission. Whilst the down- 
ward prolongation into the hypocotyl might easily result from the increased 
importance of the bundle when supplying a distinct cotyledon, the restora- 
tion of complete symmetry by the development of new laterals would be, in 
the absence of cognate evidence, an unwarranted assumption. It must be 
concluded, therefore, that the evidence available renders this alternative an 
extremely improbable one. 
The possession of lateral bundles would accord with the second possible 
method of origin, namely, by the displacement of an epicotyledonary leaf, 
since these also typically possess a median bundle flanked by two laterals. 
The epicotyledonary whorl, however, presents a perfectly normal appearance 
consisting of two members (a condition found also in some of the normal 
tricotyls), whilst a further difficulty is presented by the fact that, since 
some forms are hemitricotylous and one secondarily dicotylous, it would be 
necessary to assume not only that the leaf had undergone displacement, but 
also that it had fused with one of the cotyledons. 
It must be noted also that wherever among Angiosperm seedlings the 
strands of epicotylar leaves play any important part in the hypocotyl, they 
show rotation and are connected with a root pole, as is reported by Davey (5) 
in Juglans nigra> and by Compton (2) in Caesalpinia sepiaria and Pitheco- 
lobium Unguis-cati . No signs of doubleness have, however, been observed 
in the vascular bundles of the epicotyledonary leaves in Centranthus . 
As both the first and second alternatives seem to be excluded by the 
evidence at hand there remains only the third method of origin. The ' 
possession of laterals, and the frequent persistence of the metaxylem 
elements at least of the bundle throughout the major portion of the 
hypocotyl, accord with this interpretation, as does also a temporary slight 
division of the phloem in one instance, but no evidence as to the cause of the 
anomalous behaviour shown by the type f3 cotyledon is supplied by the 
material available. 
There remains to be discussed the so-called hernitetracotylous seedling B, 
which showed double structure throughout. Twin seedlings of this type 
have been described by de Vries (10) in Amaranthus speciosus , Datura 
