THE GENUS EQUISETUM. 187 



losiphonic axes, in which the tubuhir vascuhir axis is interrupted by foliar hicunae 

 occurring above the points of exit of the traces of tlie hirge leaves, and cladosiplionic 

 axes, in which there are no foliar lacunae corresponding to the palingenetically micro- 

 phyllous leaves, but which on the contrary are characterized by raniular lacunae 

 appearing immediately above the departing traces of the branches. As regards the 

 general morphology of vascular strands the writer, as a result of his study of development, 

 returns to the standpoint of Sachs and De Bary. 



2. Tlie writer finds, with Goebel and Buchticn, that the gametophyte of the Equise- 

 taceae, in its vertically-growing ticshy axis and its characteristically numerous thin 

 lateral lobes, presents a detailed and striking resemblance to the green autotrophic 

 species of prothallia of Lycopodium viz., those of L. inundatuml and L. cermmm. 



■ Further, the archegonium of the Equisetaceae resembles that of the isosporous Lycopods 

 in being uniformly without the basal cell, which is invariably present in the archegonia 

 of the isosporous Filicales. The embryo of Equisetum hiemale, tlie only species fully 

 studied by the writer, agrees with those of Lycopodia described l)y Ti-eub and more 

 recently by Bruchmann, in the fact that both root and shoot originate from the upper 

 (epibasal) region. Further, the sporophy tic phases of the two groups also present a close 

 agreement, since in both cases there are, invariably, microphyllous leaves and strobiloid 

 fructifications. 



3. In Archaeocalamites the internodal lacunae of the vascular cylinder occurred 

 above the branches (as may be learned from PI. 2G fig. 15), and the leaves were 

 inserted at the nodes without lacunae in the course of the continuous vascular strands. 

 This genus was consequently cladosiphonic and in this respect resembles the higher 

 Lycopods. During the phylogenetic development of the Calamites the segments of 

 the stem were gradually I'otated on each other, as has been shown by Stur, and as a 

 consequence of this process the ramular lacunae were ultimately shifted, so as to coincide 

 with the leaf-traces, but the latter give evidence of their true affinities, even in the 

 modern Equiseta (PI. 20, fig. 16), by the fact that their apparent foliar lacunae are 

 separated from them by the whole depth of the nodal wood. Moreover, the writer's 

 examination of the development of the young stele in Equiseta shows, that it is primi- 

 tively tubular and not, as Van Tieghem suggests, dialydesmic. The data of phylogeny, 

 ontogeny, and anatomy consequently all favor the view that the Equisetaceae are, like 

 Selaglnella laevigata and Lepidodendron harcouriii, cladosiphonic, and there are thus 

 additional reasons for regarding the Lycopodiales and Equisetales as closely allied. 



4. The Sphenophyllales are the protostelic ancestors of the Equisetales and agree 

 with them closely in all particulars, except the structure of their stele. But as has 

 been pointed out, protostely and siphonostely may occur in different genera of the 



