184 



EDWARD C. JEFFREY ON 



was protostelic and L. harcourtii was siphonostelic, likewise Sigillaria vascularis and S. 

 puleherrima had protostelic axes, while on the other hand S. diploxylon, S. elegans, and 

 S. spinulosa had siphonostelic axes; a similar relation exists between Selaginella martensii 

 and S. laevigata. In other instances different genera of the same natural order may exem- 

 plify the two types of stelar structure e. g., in the Gleicheniaceae, Gleichenia is protostelic 

 and Platyzoma is siphonostelic. Similar examples are afforded by the Hymenophyllaceae 

 and Schizeaceae. 



The Ancestors of the Equisetaceae. 



In this connection the question may properly be asked where are the protostelic 

 Equisetales to be found. The Sphenophyllales immediately suggest themselves in reply to 

 this question. Stur (op. tit., p. 17) and Rothpletz (Botanisches centralblatt, Gratis 

 beilage 3, pi. 11), have both called attention to their remarkable external resemblance to 

 Archaeocalamites in their strobloid fructifications, their rigid and articulated stems, and 

 whorled superposed dichotomous leaves. The branches of the Sphenophyllales also 

 resembled those of the Equisetales in rising at the nodes, between the leaves (Renault, op. 

 cit., texte, p. 170). Solms-Laubach (op. cit.) has described the sporangiophores of Boio- 

 manites romeri as peltate and Scott (op. cit., 1897, B.) has compared the much more com- 

 plex sporophylls of Cheirostrobus with those of the calamitean Palaeostachya, and makes 

 the important suggestion that the comparison of the cone of the Equisetales with that of 

 Cheirostrobus is likely to change considerably our views of the morphology of the former. 

 He probably has in mind the extension of the comparison to Calamostachys, Paracalamo- 

 stachys, Cingularia, etc., where the sporangiophore does not immediately suggest itself as 

 the ventral segment of the sporophyll, as it does in Palaeostachya. Even in the latter 

 genus the sporangiophore more often as in the case of the sporangium of the living Sela- 

 ginella (Goebel, Bot. zeit., 1881, p. 697; Bower, Phil, trans, roy. soc, 1894, B., p. 523), 

 appears to originate from the axis than from the ventral surface of the dorsal sterile seg- 

 ments. Weiss (Steinkohlen-Calamarien, Heft 2, p. 7) has pointed out that it is possible 

 to arrange a series of calamitean cones, starting with forms which have the sporangiophore 

 attached to the base of the dorsal segment, and ending with those which have it high up 

 on the axis. It is interesting to note in this connection, that the number of vascular 

 bundles in the axis of all calamitean cones yet examined is not greater than the number 

 of sporangiophores, while the so-called sterile leaves are frequently twice as numerous as 

 the vascular strands and consequently as the sjDorangiophores (Calamostachys) . This 

 feature, together with the fact that the sporangiophores were placed above and between 

 the members of the reduplicated sterile whorl, and the fact that the nodes correspond in 



