the Genus Hottonia. 263 
this point. The characteristic glandular hairs occur on all parts of the 
seedling except the roots. 
Fig. 18, PL XXI, represents a transverse section of a at Fig. 17 and 
shows the two cotyledons (c) and the remains of the seed coat, which is 
differentiated into a dark, structureless outer portion (s) and an inner 
parenchymatous layer (int.). In spite of a certain amount of shrinkage, due 
to the fact that the material was not fixed for cytological investigation, the 
cotyledons are seen to be surrounded by naked, nucleated protoplasm 
(n.fl ), which can be traced to the inner cells of the seed coat. The cell-walls 
of the latter are partially dissolved, apparently by ferment action : and, as 
if to resist the softening action on their own tissue, the outer walls of the 
cotyledonary epidermal cells are here and there clearly cutinized (< c.t .). 
Each cotyledon is traversed by a single median bundle, consisting of 
very few vascular elements with no apparent bundle sheath. Immediately 
at the base of the cotyledons, the two bundles fuse to form the stele of the 
hypocotyl, which is root-like in structure, as the xylem groups unite to form 
Text-fig. 6. Xylem, shaded ; phloem, white ; protoxylem, x. 
a diarch plate in the cotyledonary plane, while the phloem groups each 
divide, the branches fusing in pairs, so that the new phloem groups occupy 
positions on each side of the xylem plate (Text-fig. 6). 
There is little to show that the latter is, strictly speaking, diarch, since 
the few wood elements are all spiral in character and nearly the same size, 
but Fig. 19, PL XXI, which shows a consecutive series of sections (a ... e) 
through the xylem of one bundle at the base of a cotyledon, indicates 
a transition to exarchy as the hypocotyl is reached (e). This is supported 
by longitudinal sections, for though none were obtained which passed 
exactly through the median plane of the xylem plate, those at right angles 
to this direction indicated that the tracheides at each pole were of a looser 
spiral type than those in the centre. 
Text-fig. 6 is a diagrammatic representation of the transition from stem 
to root structure, which takes place in the space of about ^0 mm - at the 
base of the cotyledons, so that Hottonia seedlings conform to the type 
defined by Miss Thomas ( 13 ) as that ‘ in which a diarch root stele is formed 
at or immediately below the cotyledonary node, entirely by the two coty- 
ledonary traces, so that the whole or nearly the whole of the hypocotyl 
possesses a central cylinder of typical root structure 5 . When this type was 
first described in 1903, it was thought to be uncommon and probably 
