Seedling Structure of Gymnosperms. IV. 323 
large ; just above the cotyledonary node they fuse together to form a tube. 
The lower end of the hypocotyl bears on one side a spade-like projection, 
the foot or sucker, which remains embedded within the endosperm, from 
which it absorbs the stored nourishment. The foot consists entirely of 
parenchyma, and contains no vascular tissue ; it resembles pretty closely 
the hypocotyledonary outgrowth which occurs in a similar position in 
certain Angiosperms, e. g. Mirabilis multiflora. 
The epidermis is covered by a cuticle which is very thin except over 
the guard-cells of the stomates, which are sunken slightly below the general 
level of the epidermis and occur on both surfaces of the leaf. The meso- 
phyll is but feebly differentiated into palisade and spongy parenchyma, and 
the air spaces are but poorly developed. Some of the mesophyll elements 
are practically devoid of contents; these cells occur more especially along 
the lateral edges of the cotyledons and around the larger bundles. Our 
material was insufficient to enable us to examine older cotyledons for these 
particular cells ; in the young seed-leaves they appear rather like immature 
fibrous elements (Plate XXII, Fig. 4, a). 
The number of bundles in each cotyledon varies ; usually there are 
four larger strands with a number of much smaller traces between, the 
venation being parallel. The smaller bundles freely anastomose, and 
towards the base of the seed-leaves, they fuse on to the larger traces, so that 
four bundles from each cotyledon enter the hypocotyledonary axis. 
The structure of these vascular strands is quite normal; they are 
endarch and collateral throughout their whole length, and there is some 
cambial activity ; the tracheae frequently have very thick walls, and in 
transverse section present an appearance much like some of the metaxylem 
elements of certain Cactaceae (Plate XXII, Fig. 4). 
Transition. 
From each seed-leaf four strands enter the axis so that, at the top of 
the hypocotyl, there are eight vascular bundles arranged in four pairs 
(Diagram 3, Figs. 1 and 2). The members of each pair very quickly fuse 
together, and rotation immediately begins. The xylem-masses of each of 
the now two bundles, derived from one and the same cotyledon, face each 
other in a manner which strongly recalls the appearance presented by the 
corresponding structures in Ephedra (Diagram 1, Fig. 2, and Diagram 3, 
Fig. 3). Each strand now gradually rotates outwards, a movement which 
ultimately brings the four protoxylem groups into the exarch position. 
At the same time the protoxylems tend to become diffuse, and new 
protoxylem elements may make their appearance in the ground tissue ; 
these, at first, are not in continuity with the same tissue derived from the 
cotyledons (Plate XXII, Fig. 5). At about this level the cambium is very 
conspicuous, and extends in such a manner as partly to enclose the phloem. 
