LYGINODENDRON 361 



sclerenchyma appears in the form of dark radial bands 

 (see Figs. 129 and 130). A few parenchymatous 

 layers terminate the cortex towards the exterior. 



The course of the vascular bundles through the 

 stem is an important feature. The xylem-strands sur- 

 rounding the pith constitute the downward continuation 

 of the same leaf-trace bundles, which we find passing 

 gradually outwards through the pericycle. That this 

 is so is proved by our frequently meeting with the 

 bundles in an intermediate position, on their way 

 through the zone of secondary wood, which intervenes 

 between pith and pericycle (Fig. 129, l.t}). When the 

 leaf-trace is once clear of the secondary wood, it rises 

 very steeply through the pericycle, following, as already 

 mentioned, a nearly vertical course, but still passing 

 slowly outwards, so that the pericycle is eventually 

 bulged out to make room for it (see Fig. 129, l.t. b ). 

 The trace, which on starting is a single bundle, divides 

 into two, during its passage through the pericycle. 

 The twin-bundles thus formed are very characteristic 

 of the plant (see Figs. 129, l.t?-l.t?, and 132). The 

 double trace finally bends out sharply through the 

 cortex, and enters the base of a leaf-stalk (see Fig. 



136). 



It is a very constant rule that, in any transverse 

 section of the stem, five leaf-traces are present outside 

 the wood. They are not all equally far out, and in 

 good sections it is easy to tell which of them is nearest 

 its exit into a petiole, and which is only just leaving 

 the wood, and, in fact, to determine the exact order of 

 all five (see Fig. 129). If we begin with the trace 

 farthest inwards (l.t. 1 in Fig. 129), we find that the 



