216 PKACTICAL BOTANY. 



with the leaf- sheath surrounding it. If these parts 

 be in their natural position, it will be seen in this first 

 section that the vascular bundles of the leaf- sheath 

 alternate in position with those of the internodes. 

 Passing the sections successively under observation, it 

 will be seen that each bundle of the internode divides 

 into two branches, which diverge and insert themselves 

 respectively right and left on bundles of the leaf-sheath, 

 at the point where these curve into the axis, and begin 

 their downward course through the next internode. 

 Thus the course of each bundle of the leaf-trace is 

 simply this : it passes from the leaf-sheath into the 

 axis, traverses one internode, and at the next lower 

 node it forks, the branch bundles inserting themselves 

 on bundles entering at that node. 



These facts, together with external observation of 

 the ridges of the leaf-sheaths and internodes, will 

 suffice for the construction of the whole bundle-system 

 of the shoot of E. arvense, which is also typical of 

 the whole group. 



The bundle-system may be actually demonstrated by dissection 

 in the stem of one of the larger forms, viz., E. Telmateia. Take 

 a fresh and well-grown shoot, and cut from the thickest part of 

 it a piece about four inches in length, and including a node : then 

 remove from it the outer tissues, and scrape the soft parenchyma 

 away till the vascular bundles are laid bare ; then slit the hollow 

 stem longitudinally, flatten it out, and carefully scrape away the 

 softer tissues from the inside till the vascular bundles are clearly 

 seen ; then treat for some hours with alcohol to remove the air 

 bubbles from the intercellular spaces, and warm gently in weak 

 solution of potash : the preparation may be preserved in glycerine, 

 or in glycerine jelly. If such a preparation be carefully made it 

 will show the course of the vascular bundles in the internode, as 

 well as the branchings and fusions at the node. 



