de Fraine .— The Seedling Structure of certain Cactaceae. 137 
seed-leaf-bundles showed bifurcation and rotation of their phloem, and 
the cotyledonary bud-bundles rotated and moved outwards to meet the 
incoming cotyledon-traces and finally fused laterally with them. The 
four epicotylar strands played no essential part in the transition, they 
merely passed outwards and fused with the ' double ? bundles. The 
behaviour of the vascular tissue is thus precisely similar to that illustrated 
for Cereus tortuosus (Diagram 5, Figs. 1 and 2). The phloems and the 
metaxylems of the ‘ double ’ bundles thus produced separate and rotate 
round the protoxylem, which they thus leave exposed in the exarch position, 
and the root is again of the Cereus type. 
Cereus. 
The seedlings belonging to this genus show a considerable advance 
in succulence when compared with Opuntia , while at the same time they 
exhibit a marked diminution in size. The somewhat long and slender 
hypocotyl characteristic of Pereskia and Opuntia is replaced 
by a shorter, swollen structure in the species of Cereus. The 
cotyledons are no longer leaf-like, but are small, pointed and 
succulent, and are set slightly apart, with the inner line of 
their broad bases parallel. The two cotyledons of a seedling 
still show a difference in size, though this feature is not so well 
marked as in Opuntia , Nop ale a, and Pereskia ; the whole seedling 
is indeed slightly asymmetrical (Fig. 8). Towards the base of 
the cotyledons a small embryonic bud, bearing a few multicellular 
hairs, appears at the middle of their ventral surface. The struc¬ 
ture of the seed-leaf is very simple. It consists of a mass of 
large, rounded, parenchymatous cells, with extremely small 
intercellular spaces, and it is traversed by a small vascular bundle, which, 
towards the base of the cotyledon, may be reinforced by two still smaller 
lateral strands, and by an inner bundle which formed the vascular supply 
of the cotyledonary bud. The epidermal cells in some species, such as 
C. tortuosus , C. triangularis , and C. Jamacaru , show a differentiation into 
small rectangular cells, which appear in groups consisting of one to six 
elements in transverse section, and much larger cells in which the outer 
wall is either convex or somewhat elongated. C. peruvianus and C. 
Spachianus , on the other hand, show no such differentiation, and the 
epidermal system in these species is composed of large cells with a distinctly 
convex outer wall. As in all the other genera examined, the stomata are 
of the usual Cactus type ; they have subsidiary guard-cells, are on a level 
with the general epidermal surface, and, where a differentiated epidermis 
occurs, the stomata are restricted to the areas of the small rectangular 
elements. The hypocotyl is at first oval, but rapidly becomes circular 
in transverse section ; it is made of very large, rounded, parenchymatous 
Fig. 8 . 
Cereus 
tortuosus. 
x 2. 
