182 EDWARD C. JEFFREY ON 



Heft 1, p. 121) sliow.s clearly that the roots ami branches were on the same side of 

 the nolle in the Calamitcs, externally as well. In the center of the figure to the left are 

 seen a few small leaf-scars. Along the rest of the nodal line these have disappeared. 

 Below the indications of leaf-traces stretches a line of scars, the smaller of which are root- 

 scars the single larger one is a branch-scar, below which are the less distinct scars of its 

 basal I'oots. 



Assuming the correctness of the various arguments employed in attempting to solve 

 these difficult questions of calamitean anatomy, the result is reached, that in the Calamites 

 the branches and their morphological equivalents, the rhizophoric organs, had the same 

 relation to the nodes as in living Ec[uiseta. Further, tlie branches were more or less 

 exactly centered on the node according as they were of greater or smaller size. The 

 rhizophoric oi'gans were attached along the lower margin of the ring of nodal wood, and 

 their cylindrical medullary cavities, which, unlike those of iu>rnial branches, did not 

 expand are consequently represented on the casts by nodules situated below the 

 nodal constrictions. The infranodal tu))ercles are thus only to be found on subterranean 

 stems, and this is in accordance with Weiss's statement {op. clt., Heft 2, p. 24) referred 

 to in the Introduction, that they are absent or inconspicuous on axes, which are clearly 

 recognizable as aerial. 



An attempt has been made in the foregoing jiaragraphs to explain certain featiu'es 

 of the Calamites by reference to the corresponding features of living Equiseta. The 

 writer will now emjjloy the reverse method of attempting the explanation of certain 

 structural features of the extant genus Equisetum by a consideration of the homologous 

 ones of the ancestral and extinct Calamites. 



The Cladosipiioxy of the Equisetaceae. 



Attention has heen called in the early part of this essay to the peculiar relations of 

 the leaf-traces in Equisetum to the nodal wood viz., that they originate below it and yet 

 without causing any gap or lacuna in its vascular ring, as might be expected from the 

 analogy of the foliar lacunae of the Filicales, which occur immediately above the exit o£ 

 the leaf-traces from the vascular tul)e. Yet, notwithstanding the fact that the lacunae do 

 not begin at the level of exit of the leaf-traces, they do, nevertheless, occur opposite the 

 outgoing traces, Ijut ordy make their appearance above the nodal wood. These facts 

 have already been referred to in connection with photographs 5 and G (PI. 28, figs. 5, G) . 

 They appear not to have Ijeen noticed by previous writers and are susceptible, neverthe- 

 less, of a somewhat interesting interpretation which is of importance from the stand- 

 point of the phylogeny of the Equisetaceae. 



