THE GENUS EQUISETUM. 175 



as to pass through the very base of the branch, there is still a wide brini of noilal wood 

 above the latter. The leaf-traces, as may be learned from the examination of a series of 

 tangential sections, originate on a level with the lower surface of the branch-traces, 

 but as they pass outwards, rapidly i)ass above the latter, as may bo inferred from 

 photograph 2 (PI. 29, fig. 2). 



A deep tangential section is likewise represented in photograph 4 (PI. 29, fig. 4). 

 The arrangement of the bundles at the sides is the same as in the preceding photograph, 

 but the two central bundles, between which a cluster of thick-walled cells indicates 

 the starting-point of the medulla of a branch, do not alternate but are continued with 

 those of the iuternode above. This [jhenoiuenon is not rare in E. hiemale and is of 

 interest both because it has apparently not been noticed before in Equiseta, and because 

 it exemplifies a mode of fascicular arrangement which was common at the nodes of the 

 Calamites. 



Ratlial sections show more clearly tlum tangential ones the relations of the branches 

 to the nodal wood, and it is the more necessary to devote some attention to these 

 features, because the opinion prevails tliat the branches of the Calamites in contrast to 

 those of E([uiseta originated above the node. Photograph 5 (PI. 29, fig. -5) shows the 

 topography of a radial section of an aerial stem of E. hteumle, at the point of origin of a 

 branch. At d is the partially sclerified nodal di;i})hragm of the main stem, and below it 

 at n is the nodal wood. From the lower half of the nodal vascular ring comes oft' a 

 branch, c. The diaphragm of the first node of the branch is very deep, and is somewhat 

 sclerified at the ends. Two roots, >•, and a nodal bud, k, are attached to the basal node of 

 the branch. The first leaf-sheath, or ochreola, is present interiorly, but is abortive on the 

 upper axial side. It is manifest that the aerial branch of E. hioiiale arises neither above 

 nor below the node but from the lower region of the nodal wood. Photograph 6 (PI. 

 20, fig. G) illustrates the topography of the origin of a rhizophoi'ic bud from a node of 

 the rhizome. The same general features olitain as in the last photograph, and it may 

 readily be seen that here, too, the potential secondary axis originates from the lower 

 region of the nodal wood. The lettering is the same as in the preceding photogi'aph. A 

 feature which is worthy of note is that, the first sheath of the bud, the future oclu'eola, is 

 normally developed, as is generally the case in branches derived from the subterranean 

 stem. The next photograph 1 (PI. 30, fig. 1) illustrates the mode of origin of a stout 

 upright branch from a deep horizontal rhizome; as before, d is the diaphragm, n is the 

 nodal wood, and r is a root. Here, too, the branch arises neither above nor below the 

 node l)ut from the nodal wood, and since in this case the base of the secondaiy axis 

 is very broad, it covers the whole of the node. 



The next photograph 2 (PI. .'Jd, fig. 2) is of a radial section through the nodal 



