576 Davey.— Seedling Anatomy of certain Amentiferae. 
The chief aim of the investigation has been to record the earlier phases 
of primary differentiation of vascular tissue in the seedlings. To this end 
the material has been cut as far as possible in the youngest stage in which 
such differentiation could be demonstrated. Owing to differences in habit 
and rate of growth, correlated with differences in the rate of succession 
of the phases of vascular development, it is not possible to fix or exactly 
define any one stage which shall be equally applicable to all the seedlings. 
The types of seedling include, on the one hand, slender epigeal 
forms in which the cotyledons are elevated above the soil by intercalary 
elongation of the hypocotyl, development of the plumular bud being mean- 
while retarded (e. g. Alnus, Carpinus , &c.) ; and, on the other hand, massive 
hypogeal forms (e. g. species of Juglans , Castanea , &c.) in which the 
axis of the plumule may be more or less well developed in the seed. 
In these forms growth at first takes place almost simultaneously in both 
hypocotyl and epicotyl, but subsequently the latter elongates rapidly while 
the former remains very short. 
In the first case there exists a well-defined stage during which the 
plumular strands are not sufficiently differentiated to exert any influence 
on the essential structure of the vascular system of the hypocotyl, and 
description of transition phenomena involves only the vascular strands 
in primary root, hypocotyl, and cotyledons. 
In the second case there is no stage in which the plumular influence can 
be thus non-existent, since the earliest primary differentiation of vascular 
tissue will extend throughout the root, hypocotyl, and epicotyl. ‘ Tran- 
sition 5 here includes the connexion of the vascular system of the root 
and of the hypocotyl with the early leaves, both cotyledonary and 
plumular. 
In both cases cambial development may begin so early in the region 
of the cotyledonary node that primary differentiation is obscured, and 
in some cases can scarcely be said to exist. 
The most striking anatomical feature of the forms under consideration 
is the absence of that uniformity of structure which has been found to be so 
pronounced in other groups. The variations which occur relate to number 
and position (these factors being to a great extent correlated) of the proto- 
xylem poles in hypocotyl and root, All the modifications may be referred 
to Type 3 of Van Tieghem, in which transition from stem to root structure 
is brought about by ‘ movements ’ of the phloem strands while the xylem 
centres remain fixed. 
In describing the various types of structure the terms Cruciform and 
Diagonal (see Fig. i) will be applied in the sense in which they are used by 
Dr. Thomas 1 in her recent paper. 
1 Thomas, E. N. : Seedling Anatomy of Ranales, Rhoeadales, and Rosales. Ann. of Bot., 
vol. xxviii, 1914, p. 698. 
