195 
Seedling Structure of Gymnosperms . II. 
In other instances, a different course is pursued. In the upper part of 
the axis two of the cotyledonary traces fuse together, and, at a slightly 
lower level, two others effect a junction, so that six bundles result which 
by rotation of the xylem and fusion of the phloem, as in the case first 
described, form a triarch root. (Diagram 2, Figs. 1,4 ,5 and 6.) 
The first seedling of the plant under consideration clearly represents 
an instance of four cotyledons having split to form eight ; while in the 
second case, six of the seed-leaves represent half-cotyledons, and the two 
which play no prominent part in the transition are to be considered 
subsidiary seed-leaves. 
Abies amabilis , Forb. The one available seedling of this plant had 
eight seed-leaves which fused to form a short cotyledonary tube. 
The transition-phenomena took place in a similar manner to those in 
A. sibirica ; the bundle of one cotyledon played no part in the process, and 
thus is to be placed in the category of subsidiary cotyledons. Of the 
remaining bundles, each formed a pole of the root, which organ was 7-arch 
in the higher region, but was reduced to 6-arch, and finally 5-arch. 
Abies magnified var. Shastensis. Here, again, only one seed germinated, 
giving rise to a seedling with nine cotyledons. The transition resembled 
both A. sibirica and A. pectinata. The bundles of six of the seed-leaves 
underwent bifurcation of the phloem and rearrangement of the xylem to 
form six poles of the 7-arch root, two of the cotyledons behaved as in 
A. pectinata, and together formed the remaining pole of the root, the 
remaining cotyledon merely fused with its immediate neighbour and played 
no further part. Thus of the nine seed-leaves, six represent whole- 
cotyledons, two are half-cotyledons, and one is subsidiary. 
The 7-arch root was reduced to a 6-arch structure by the gradual 
disappearance of one phloem mass, and the fusion of the two protoxylems 
originally separated by the obliterated bast. 
PlCEA. 
The cotyledons do not call for much comment. In transverse section 
they are triangular in shape ; the mesophyll is very loose with a few 
secretory cells ; the transfusion tracheides are not very numerous, and are 
more abundant in P. ajanensis and P. morinda than in P. mgra ; resin 
ducts are absent ; and fibrous elements occur on the dorsal side of the 
phloem, they are not, however, so numerous as in Abies. Each seed-leaf 
has one endarch vascular strand which shows no vascular rearrangement 
until entry into the hypocotyl has been gained. The cotyledons, at their 
basal regions, may fuse together laterally to form a more or less well-defined 
cotyledonary tube ; P. ajanensis has the tube fairly well defined, P. morinda 
less so, and in P. nigra there is no lateral union of the seed-leaves. 
P 
