90 MR. R. H. COMPTON : AN INVESTIGATION OF THE 
a group as the Filicineæ, for instance, where the juvenile anatomy has 
yielded results of such great phylogenetic value. In the Filicineæ there is 
no such break in ontogeny as occurs between the unfolding of the Phanero- 
gamic seedling and the growth of the epicotyl. In the Phanerogams the 
plant hardly begins to “live its own life” unti! the development of the 
plumule ; the seedling is comparable with the larva of an insect, with habits 
and structure distinct from those of the mature organism. 
In the present state of our knowledge of anatomy, however, & priori 
arguments count for little. It 15 impossible to decide how much weight to 
give to a fact emploved as a phylogenetic criterion unless its dependence on 
adaptation or the direct influence of the environment is taken into account. 
This paper aims at elucidating some of the relations which obtain between 
the anatomy of a seedling on the one hand and its size, the relative develop- 
ment of its parts, &c. on the other. It thus tends to sift out palingenetic 
from cenogenetie influences, and to provide a surer basis for the discussion 
of apparent relationships between different species in respect of their 
seedling anatomy. 
THE NATURE OF THE Hypocortyt. 
The hypocotyl is a serious stumbling-block to rigid morphologists, and 
various views have been put forward as to its nature and characteristics. 
The point of view to which the writer has been led must be briefly 
explained. 
No exact definition of the hypocotyl as a morphological entity is to be 
anticipated; even the root and stem, between which the hypocotyl is 
intermediate, have never been defined unequivocally. If we take a broad 
view of the evolution of plant-members we are compelled to regard the 
hypocotyl, not as a new intercalated organ, but simply asa segment of the 
primitive axis. Its peculiarities are due to its position as intermediary 
between root and stem. The primitive protostele of the whole axis of many 
Filicales, Sphenophyllales, е. has its representative in the root only of 
Angiosperms ; the vascular system of the stem has undergone considerable 
evolution. As we ascend the continuous axis from root to stem, we pass 
from a primitive to an advanced vascular structure, traversing a region of 
intermediate complexity on the way. This region represents (Chauveaud, 
1911, p. 433) an intermediate stage of vascular evolution ; just as does, for 
instance, the solenostele in the passage from protostely to dictyostely in the 
ontogeny and phylogeny of certain ferns. 
This transition in the Phanerogams is bound up with the vascular 
supply of the cotyledons and leaves, just as in the Filicales, but the axis may 
be considered to a large extent independently of the leaves in both cases. 
