729 
Seedling Anatomy of Certain Sympetalae . 
bearing a large thin lamina with retuse apex. A definite midrib traverses 
the blade, and gives off a pair of branches before bifurcating near the apex. 
Thus each lobe of the cotyledon is supplied with two principal branch veins. 
Near the apex are ramifications of smaller vascular strands consisting solely 
of spiral vessels or tracheides, which end in curious cavities forming a kind 
of hydathode ( 24 ). The point of attachment of the seed-leaves is marked 
by a large swelling, but there is no cotyledonary tube. 
Transverse sections of the lamina show the midrib with the lateral 
veins and their branches (Diagram i, Figs, i and 2). The mesophyll is 
differentiated into palisade tissue and spongy parenchyma, and at various 
points are large secretory cells with vascular connexions. Coming down 
the lamina the lateral strands join on to the midrib. Anastomoses occur at 
the junction of blade and petiole and occasionally lower down, and in the 
Diagram 1. Convolvulus tricolor, var. major. Transition from cotyledons to root. In Figs. 3-7 
and in the following diagrams, protoxylem is shown in black, metaxylem dotted, and phloem hatched. 
upper part of the latter there is a large median bundle and two small 
laterals, all simple and collateral in structure. While still in the petiole the 
median strand divides, two groups of xylem and phloem moving away right 
and left, leaving a small protoxylem strand between them. In this condi- 
tion (Diagram 1, Fig. 3) the bundles enter the hypocotyl, where the small 
lateral strands (a and A'), increased in size by the appearance of metaxylem 
elements, move towards their fellows (b and b') from the other cotyledon, 
the protoxylems turning outwards during the process (Diagram 1, Fig. 4). 
The protoxylem groups of these bundles become detached from the meta- 
xylem masses, and taking up a position between the latter, they fuse 
together, and traverse nearly the whole of the hypocotyl in this condition 
(Diagram 1, Fig. 5). The group corresponding to the midrib, on the other 
hand, decreases in size, and while travelling down the hypocotyl its con- 
stituent parts assume different positions, and are not always well defined. 
