Anatomy of Teratological Seedlings . IV. 487 
the first plumular leaf. The possibility of the dicotyledonous embryo 
being a fusion twin is rejected on the vascular evidence which shows that 
‘ it is merely a slight modification of the monocotyledonous one and gives 
no suggestion of the fusion of two embryos \ 
In Cyrtanthus sanguineus (8, 12) the embryo, prior to maturation, passes 
through a phase in which the cotyledonary tube shows division into four 
shallow apical lobes, each of which is supplied by an independent procambial 
strand. The lobes are obviously in pairs, one of which is slightly smaller 
than the other. This stage Coulter and Land regard as representing a 
tetracotylous condition. It is followed by a stage in which, owing to 
a more active growth of the cells of the cotyledonary zone lying between 
the growing points of each pair, a union in twos occurs, this being accom- 
panied by an elongation of the sheath. This stage is interpreted as 
a dicotyledonous condition. Subsequently one ‘ cotyledon ’ develops rapidly 
whilst the growth of the other ceases, so that a monocotyledonous mature 
embryo is produced in which the originally independent vascular strands 
from the shorter side bend sharply to unite with those supplying the 
elongated portion. In a further contribution Coulter (7) extends the 
theory to the Gramineae, homologizing the epiblast with the second reduced 
cotyledon, and the scutellum with the dominant one. A series is described 
ranging from species such as Zizania aquatica and Oryza sativa , in which 
the epiblast is well developed, through those showing a small epiblast (e. g. 
Triticum vulgar e ), to species like Zea Mays , in which it is absent. These 
are interpreted as illustrating the progressive stages in the abortion of the 
second cotyledon. 
It will be noticed that Coulter and Land’s theory rests upon three 
assumptions, namely that — 
(a) The massive proembryo is more primitive than the filamentous one. 
(b) The earlier and intermediate stages in embryogeny have a profound 
phyletic significance. 
(< c ) The phyletic value of the vascular structures is negligible. 
All three assumptions are at least debatable, and the third seems open 
to serious objections. It is plain that the denial of the phyletic value of 
vascular structures in phanerogamic seedlings carries with it the onus 
of supplying an adequate alternative explanation for certain well-defined 
anatomical characters. Two examples of this kind may be cited. It is 
a matter of common knowledge that the hypocotyl in its young stages 
usually shows an exarch position of the protoxylem elements and a radial 
grouping of the xylem and phloem, this being subsequently replaced by 
a collateral grouping of the vascular tissues owing to the resorption of the 
first-formed elements and the substitution for them of others with a 
different orientation. The remarkable constancy with which this cycle is 
repeated in all phanerogamic groups (4) creates a strong prima facie case 
