178 THE AMERICAN MIDLAND NATURALIST 
‘leaflets have a tendency of unequalization of halves, but especially 
it is the apical leaflet that is inequilateral. 
ANATOMY OF THE SEEDLING. 
The primary root has a single radial woodbundle that con- 
tinues partly through the hypocotyl and gives off two branches for 
the petioles of the cotyledons. The main part continues into the 
epicotyl and from this collaterals are given to the leaf petioles 
as soon as they appear. The stele of the hypocotyl] in cross section 
is diarch exarch. 
PRIMARY Root. (Fig. 3). 
A cross section of the pirmary root shows the woodbundle 
to be radial, diarch and with apparently a continuous strand of 
xylem (Xy) having phloem on both sides (Ph). The growth 
of xylem is exarch and the ducts are spiral and annular. The 
endodermis (En) is regular and clearly differentiated by the size 
of cells. In shape the cells are in no way different from the sur- 
rounding cortex but do not have Casparyan spots, a common 
peculiarity of this tissue. In very young plants the periblem (GR} 
is composed of about four layers of cells which increase in size 
outwards and merge into a series of more or less flattened cells 
which constitute the hypodermis (Hy). The epiblema (Ep) cells 
are thick walled on their outer side and are more palisaded in 
shape than those lying below them. 
EpicotyL (Figs. 4, 5, 6.) 
The section illustrated in this figure (Fig. 4) is a very young 
stage and cut close to the root. The stele like that of the root 
is diarch exarch and the cells of the pith are very irregular in 
shape. The stele is present in the middle of the pericycle and 
this has an endodermis not well defined. The cortical parenchyma 
of about four layers shows an irregular structure in the size of 
its cells. A distinctive hypodermis is lacking altogether and 
the outer layer (Ep) consists of smaller thicker cells than the 
underlying parenchyma. 
A cross section of an older seedling (Fig. 5 shows the changes 
which occur in the hypocotyl due to later growth. The proto- 
and meta-phloem (Ph) have been pushed out by the formation 
of cambium (Ca) which now surrounds the xylem (Xy) and is 
itself enclosed by the secondary phloem. ‘The development of 
xylem is irregular and lateral to the proto- and meta-phloem. 
