SPOROPHYTE. 21 
separate this slit forms a leaf-gap in the adjacent (inner) face of each 
branch. From the lower margin of both gaps the trough-like leaf-trace 
comes off, forming for a time a connection across the fork from one branch 
to the other. It soon becomes distinct from both. Leaf-gaps are easily 
dissected out, since the tissues readily separate along the line of the endo- 
dermis. 
As stated above, the cortex and medulla of the stem come into contact 
or continuity through the leaf-gap (fig. 100). The starchy layers always 
connect, and sometimes a strand of sclerotic cells connects the outer cortex 
with the similar central medulla. In about half the nodes examined (9 out 
of 20) the sclerotic medulla passes the leaf-gap as a solid rod unchanged. 
In one-fifth (4) it connects directly with the outer cortex through the 
wide leaf-gaps. In 7 a rod of sclerenchyma passes from the medulla out- 
ward in the groove of the leaf-trace to vanish in the petiole or to become 
continuous there with a peripheral layer of similar cells. This rod may 
originate independently in the starchy medulla shortly below the node, or 
it may begin as a ridge on the sclerotic medulla, which is gradually con- 
stricted off. These different arrangements of sclerenchyma may occur at 
successive nodes of one stem. 
Between the cortex and the xylem of the stem, all of the inner and outer 
tissues become continuous around the margins of the leaf-gap—endodermis 
with endodermis, pericycle with pericycle, phloem with phloem, and con- 
junctive parenchyma with conjunctive parenchyma (fig. 108). Or, the 
phloem may become very thin, or may be completely interrupted for a 
short distance on one or other side of the gap. A transverse section of 
the stem through a leaf-gap shows the vascular system as a deep, round 
horseshoe (fig. 100). No new tissue elements are seen at the nodes. 
Spiral vessels are not found in leaf-trace or stem. The cells bend out 
from stem to leaf by gentle curves, without any noticeable peculiarities. 
Where the stem forks each tissue system remains continuous and 
unbroken (fig. 99). There is no ramular gap. Onecan best imagine the 
structure by starting with a Y-shaped object made of round rods, welded 
together below. Let this represent the sclerotic medulla. We dip the 
object into melted wax, coating it all over; this represents the layer of 
starchy medulla. Successive coatings of suitable thickness may represent 
inner endodermis, inner pericycle, inner phloem, xylem, outer phloem, outer 
pericycle, outer endodermis, starchy cortex, sclerotic cortex, and epidermis. 
In the angle of the Y the continuity of tissues from one arm to the other 
is strikingly smooth and regular. A single scalariform tracheid may 
extend fora long distance in each arm. On the sides of the fork this con- 
tinuity involves angular elements of peculiar shapes (fig. 98). 
The apex of the stem is so clothed with hairs as to appear smoothly 
rounded (fig. 3). Under this covering there is a shallow, basin-like de- 
pression (fig. 70), not often symmetrical, at the tip of the stem. A low 
