312 Mellor: The Seedling Structure of Dryas octopetala. 
that it did not seem to be tetrarch as the Rosales commonly 
are, and up to the present time I have seen no trace of more 
than two protoxylem groups in the root. The behaviour of 
the cotyledon traces on entering the hypocotyl seems to conform 
absolutely with the diarch type as described and figured by 
Miss Thomas (4). 
Fig. 1 shews a young seedling similar to the one from which 
sections for examination were made. For these I have to 
thank Miss M. M. Brierley, who cut serial microtome sections 
of entire seedlings. 
Fig. 2 shews an older seedling; the plumule has further 
developed and bears its first foliage leaves. 
The first section below the growing point of the plumule 
shews a ring of cells with crowded contents, some groups of 
which are more clearly defined and are doubtless the procambial 
strands. These continue downwards, and at a lower level 
(Fig. 3) the stem is clasped by three foliage leaves (e, d, c), 
each with one central and two lateral bundles. A fourth 
foliage leaf (b), the first above the cotyledons and so the oldest, 
has only one bundle in its leaf stalk, and that a central one. 
The ten bundles from these foliage leaves pass into the stem 
and join the cauline strands to form the vascular cylinder. 
This divides into two crescent shaped masses (fig. 4, /) just 
where the cotyledons (fig. 3, a) join the hypocotyl, and into 
the gaps thus formed the double bundles of the cotyledons 
pass (fig. 4, cb). From this point downwards the plumular 
traces become gradually reduced, and eventually die out 
altogether, while the cotyledons pass towards the centre. 
There the opposite groups of wood meet to form the xylem 
plate of the root, and the two phloem groups from each cotyle- 
don divide and re-unite in such a way as to form two lateral 
groups in the root. (Fig. 5). The four alternating strands 
of xylem and phloem can be clearly seen close to the tip of the 
root (fig. 6), the spiral thickenings of the two protoxylem groups 
standing out very distinctly in oblique sections. 
From this it appears that the root of Dryas is diarch and 
not tetrarch, as are the seedlings of the same order examined 
by Miss Thomas, and that while many members of the order 
conform to the primitive type, Dryas shews reduction such as 
we find in many Ranales. 
REFERENCES: 
(1). Miss E. Sargant. ‘A Theory of the Origin of Monocotvledons 
founded on the Structure of their Seedlings.’— Annals of Botany, 1903. 
(2). Tansley and Thomas. ‘ Root Structure in the Central Cylinder 
of the Hypocotyl.’— New Phylotogist, 1904. 
(3). Tansley and Thomas. ‘ The Phylogenetic Value of the Vascular 
Structure of Spermophytic Hypocotyls.—Brit. Assoc. Report, 1900. 
(4). Ethel A. Thomas. <A ‘ Theory of the Double Leaf-Trace founded 
on Seedling Structure.’— New Phytologist, 1907. 
(5). T. G. Hill. ‘On the Seedling Structure of certain Piperales.’— 
Annals of Botany, 1906. 
Naturalist, 
