584 Davey. Seedling Anatomy of certain Amentiferae. 
donary plane from the central strands of the cotyledons, their metaxylems 
being supplemented by that of the lateral groups. Widely extended tan- 
gential masses of metaxylem result, as the stele surrounds a very large pith. 
In the intercotyledonary plane the amount of metaxylem helping to consti- 
tute the plumular traces becomes increased, and they continue downwards 
as root poles with which the cotyledonary strands make no connexion 
(Fig. 6 , A, B, C). In the cruciform tetrarch root all the poles are equiva- 
lent, and the differentiation of their primary xylem becomes entirely 
centripetal. Groups of plumular metaxylem in the diagonal planes also 
extend into the root, and neighbouring cotyledonary phloem groups do not 
cot,, plane. 
Fig. 7. Juglans nigra „ Part of transverse section of very young epicotyl, showing one of the plumu- 
lar leaf-traces in cotyledonary plane {cot. plane), px. - piotoxylem ; ph. — phloem, x 360. 
appear to meet, perhaps owing to the large size of the stelar ring, but 
become linked by phloem developed later in connexion with plumular traces. 
The hypocotyl stele is surrounded by a well-marked endodermal sheath } 
portions of which leave the axis with the cotyledon traces. Within the 
endodermis there is a wide pericycle consisting of several layers of cells. 
Secondary thickening takes place at an early stage. 
In this seedling there has been traced the complete connexion of 
a plumular leaf with an intercotyledonary root pole by means of a vascular 
strand showing uniform structure in hypocotyl and epicotyl. Similar 
connexions have been described by Compton 1 as occurring in Caesalpinia 
sepiaria and in Pithecolobium Unguis-cati , members of the Leguminosae. 
1 loc. cit., pp. 9 and 21. 
