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phloem (G). These are connected with the adaxial endodermis of 
the next leaf-trace. During the early stages in the separation of 
the trace, the internal phloem has a curved cross-section (D), its 
concavity being occupied by an internal thickening of the xylem, 
which corresponds with the thickening of the edge of the leaf-gap 
in Dennstcedtia apiifolia. In some cases this thickening is continued 
as an isolated strand of tracheids in the internal phloem (G), and 
joins the dilatation of the xylem at the base of the next trace 
Subsequently the internal strand of xylem becomes a constant 
feature of the stele, usually separated from the main cylinder 
during the greater part of the internode, but practically always 
connecting with it at the base of the leaf-trace (H). Tracheae 
often run up from the internal strand to the point in the 
external xylem from which the last tracheids of the trace 
have departed, but do not contribute to the trace itself. The 
internal endodermis becomes a continuous strand connected at the 
nodes with the adaxial endodermis of the leaf-trace, which is now 
kidney-shaped in cross-section, the endodermis being “invaginated” 
into the concavity of the trace. Later on a ground-tissue pith appears, 
both in the leaf-trace (L) and in the stele (J), inside the internal 
endodermis. These piths are often connected with one another, 
but neither of them connect, at this stage, with the cortex. When 
such a connexion first occurs it is the pith at the base of the trace 
which first opens to the cortex. Later on the stele itself opens in 
front of the trace, forming a true leaf-gap (K.) Phloem extends from 
one side into the middle of the internal xylem-strand (M), and now 
the dorsal half of the strand frequently moves up and helps to close 
the gap made in the external xylem by the departure of the trace (N). 
Previously the gap has been closed by the edges of the external 
xylem approximating as the leaf-trace trachea; move out. An 
internal endodermal strand appears in the midst of the internal 
phloem of what may now be called the second cylinder. By this 
time the trace has become horse-shoe-shaped in section, with 
thickened ends (O), or with abaxially directed xylem hooks (Fig. 
61, R). At a slightly more advanced stage these hooks are 
elaborated into free abaxially directed limbs of the trace (S). 
The hooks or limbs are supplied with tracheae from the dorsal 
half of the internal cylinder, which now for the first time directly 
contributes to the leaf-trace (Q). In the next stage of elaboration 
the internal cylinder has acquired a pith (T), and regularly opens 
at the node, sending off a dorsal column of tissue, which fills 
