DIV. I 



MORPHOLOGY 



91 



In the Horsetails, the Coniferae, and the Dicotyledons, all the leaf -trace 

 strands penetrate equally deeply into the stem to pass down this as parts of the 

 characteristic ring of bundles evident in transverse sections. The course of the 

 bundles in the internode can thus be indicated on the surface of a cylinder or 

 represented as if this surface were flattened in one plane. Complications occur 

 at the nodes by the leaf -trace strands being joined by transversely-placed 

 cauline strands ; cross connec- 

 tions of later development often 

 occur in the internodes also. 



A relatively simple example 

 of the arrangement of vascular 

 bundles is afforded }jy the young 

 shoots of Juniperus nana (Fig. 

 113), the leaves on which are in 

 whorls of three. Krom each 

 leaf a leaf-trace consisting of 

 a single vascular bundle enters 

 the stem. This divides into 



FIG. 113. Diagram of the course 

 of the vascular bundles in a 

 young branch of Jit n iperus nana 

 shown on the unrolled surface 

 of the cylinder. At k, k the 

 vascular bundles passing to the 

 axillary shoots are seen. (After 

 GEVLER.) 



FIG. 114. Diagrammatic representation of the course of the 

 vascular bundles in a young twig of Taxus baccata. The 

 tube of bundles is slit up at 1, and spread out in one 

 plane. 



two about the middle of the internode below, and the portions diverge right and 

 left to unite with the adjacent leaf -traces. The arrangement of the bundles in 

 a young twig of Taxus baccata as shown in Fig. 114 is less simple, though in this 

 case also the leaf-trace consists of only one bundle. Each leaf-trace can be 

 followed down through twelve internodes before it joins on to another bundle. 

 It first runs straight clown for four intemodes and then bends aside to give 

 place to an entering trace, with which it later unites. In Taxus the leaf 

 insertions, and consequently the places of entry of leaf-traces, have a divergence 

 of -fg. An example of leaf-traces composed of three bundles is afforded by 

 young branches of Clematis viticella, the arrangement of the leaves on which is 

 decussate. The median strands of the leaf-traces (a and d, g and k, n and q, 

 t and x in Fig. 115) run down through one internode, dividing at the next 

 done into two arms which fuse with the adjacent lateral strands of the leaves? 



