EQUISETUM SPOROPHYTE 329 



of the internode. Note especially that, as in the inter- 

 node, so also in the leaf-sheath, one vascular bundle, 

 here of small size and simple structure, is to be found 

 opposite each ridge. 



IV. Cut a series of rather thick transverse sections 

 through the nodal region : it will be best to select 

 one which bears no fully-developed, lateral branches. 

 Keep them all in their right order of succession, mount, 

 and compare them under a lower power, starting from 

 such a section above the node as will show an arrange- 

 ment of tissues typical of the internode, together 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 two equal branch-bundles inserting 

 themselves, right and left, 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 bundle-system of 

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

 whole group. 



