174 



EDWARD C. JEFFREY ON 



internally the nodal organs, a, where these are present. The central cylinder in the 

 nodal region, as has been often described, forms a continuous ring in which the vascular 

 tissue, instead of being scanty and separated into individual bundles, each characterized 

 by an internal lacunar protoxylem, as is the case in the internodes, is massive and 

 entirely devoid of typical protoxylem elements. At the lower side of the photograph the 

 leaf-traces have quite cleared the central cylinder, and it is to be noticed as a feature of 

 importance, which will be subsequently referred to more at length, that the nodal vas- 

 cular ring is quite unbroken by their exit. In the upper part of the figure, the medulla 

 is seen to extend outwards into the root-bases. 



Photograph G (PI. 28. fig G) is of a section through the nodal region of E. arvense.- 

 The nodal organs are absent in this species, but the rhizophorie buds, c, are better devel- 

 oped than in E. hiemale and E. silvaticum. The fact that the so-called foliar lacunae do 

 not appear immediately above the leaf-traces, as they should from the analogy of the 

 Filicales, but are separated from them by the nodal wood, may also be inferred from this 

 section, which on the whole closely resembles that of E. silvaticum. Nodal organs have 

 been found by the writer only in E. hiemale and E. silvaticum, and are absent in E. varie- 

 gatum, E. arvense, and E. limosum. 



In the next photograph (PI. 29, fig. 1) is shown part of the section through the 

 node of E. limosum. In this species all the nodal buds develop as rhizophorie organs 

 except one or two. At c is the single large ramular bud and at b are the rhizophorie 

 organs. The other features of the section need not be described. 



Turning our attention now to the longitudinal topography of the stem of Equisetum 

 we have in photograph 2 (PI. 29, fig. 2) a tangential section of the nodal region of 

 E. hiemale the plane of which is sufficiently deep to lay open the vallecular canals, I, 

 of the lower internode ; a branch, c, is making its way out through one of these. The 

 magnification is sufficient to show that the medulla of the branch is composed of brown 

 sclerenchymatous cells, and that its wood, which is no doubt to be regarded as the nodal 

 wood of the first segment of the branch, is devoid of lacunae, such as occur in the 

 intern* des, and forms a ring, the vessels of which are still immature on the upper 

 side. Above the branch are present four leaf-traces, t, which are about to assume an 

 upward course in the foliar sheath of the main stem. The more profound tangential 

 section of photograph 3 (PI. 29, fig. 3) shows clearly the arrangement of the fibro- 

 vascular bundles at the node. Each bundle from the lower internode widens out at 

 the node and the contiguous strands become thus united. From this ring of nodal 

 wood the bundles of the upper internode take their origin in alternation with those 

 of the inferior internode. A branch, c, is starting from the lower border of the nodal 

 wood between two lower vascular strands, and, although the plane of section is so deep 



