86 Bexon.— Observations on the Anatomy of 
the two xylem groups. Before fusion was complete, however, the proto- 
xylem elements of one xylem mass disappeared, so that only the meta- 
Xylem fused with the neighbouring group. 
In the tricotyls as in the hemitricotyls a third type of seedling must be 
distinguished, this type being characterized by the fact that one of the three 
vascular bundles on entering the hypocotyl retained its collateral structure, 
whilst the other two bundles proceeded to undergo rotation and form 
a diarch plate. The protoxylem of the collateral bundle disappeared soon 
after its entry into the hypocotyl, and in one or two cases there was 
a movement of the metaxylem elements towards one of the xylem poles 
before their final disappearance. It was noticeable also that in some 
instances the cotyledon supplied by the collateral bundle was smaller than 
either of its fellows. In the majority of tricotylous seedlings the number of 
epicotyledonary leaves in the first whorl was three, but in a few cases two 
only were present, and in two seedlings one of the two epicotyledonary leaves 
ft was bifurcated. 
Hemitetracotyls . Of this class five seedlings only have been examined, 
and since these present several features of interest they will be described 
separately. 
Seedling A. Each cotyledon showed an apical notch which was 
slightly deeper in the one case than in the other (Fig. 5 (3 a and 3 b )). 
Each lobe of the cotyledons was supplied by a collateral vascular bundle, 
thue pairs of bundles uniting in the one case in the petiole, and in the other 
at the junction with the hypocotyl, so that at the apex of the hypocotyl two 
bundles appeared which ultimately gave rise to a normal diarch plate. 
Seedling B . This seedling as regards external appearance was almost 
identical with seedling A, since the two cotyledons each showed an apical 
cleft, and when the seedling was uprooted, it was classified without hesita- 
tion as a hemitetracotylous specimen (Fig. 5 (2, a and 1 b)). In anatomical 
structure, however, it showed striking differences from the condition described 
above. The two apparent cotyledons were* each divided for a short distance 
only, but the median bundles of the associated lamina segments remained 
widely separated throughout the length of the ‘ cotyledon \ At the base of 
the cotyledon a lateral bundle appeared on the outer side only of each main 
bundle. Just above the cotyledonary node two distinct sets of plumular 
leaves were present, each set being dimerously arranged, but whilst one 
group showed two leaves only, in the other two pairs were visible 
(Fig. 6, a). 
At the cotyledonary node each of the four main bundles rotated, and 
the opposed bundles, one from each ‘ cotyledon united together to form 
a diarch xylem plate, so that the hypocotyl contained two widely separated 
diarch steles, this condition obtaining throughout its whole length (Fig. 6, c). 
In the root region, lateral rootlets were given off from each of the steles, 
