166 EDWARD C. JEFFREY ON 



p. 170), originated at the nodes, and he tells us that they came off from the stem 

 between the leaves, and consequently like those of Calamites and Equisetaceae were not 

 axillary. 



The fructifications of the Sphenophyllales were cones of superposed verticils of 

 sporophylls. These consisted of a dorsal sterile segment, and one or more ventral spo- 

 rangiferous segments, bearing as a rule on their upper surface a single sporangium which 

 hung inwards towards the axis of the cone. Solms-Laubach (Jahrbuch geol. reichs- 

 anstalt, 18!)5, vol. 45, p. 239) has recently described an interesting strobilus, Bowmani- 

 tes romeri, belonging to tliis group, in which the sporangiophores are transversally 

 peltate like those of the cycad Encephalartos. 



Tiie most interesting cone of this class, however, is that of which Scott (Cheiro- 

 strobus, Phil, trans, roy. soc, 18U7, B.) has still more recently given an account. The 

 sporophylls of Cheirostrobus are arranged in superposed verticils of twelve members. 

 Each sporophyll consists of a dorsal and a ventral tripartite segment. The former is 

 sterile, and the latter has each of its three divisions developed into a typical peltate 

 sporangiophore bearing four sporangia. This author calls attention to the marked 

 resemblance of his cone to the calamitean Palaeostachya and Calamostachys. 



The internal features of structure in the stem of the Sphenophyllales were remark- 

 able. There was a protostelic triarch, hexarch, or dodecarch (Cheirostrobus) central 

 cylinder. The groups of protoxylem were generally distinguished by the presence of 

 carinal lacunae as in Equisetum. The central cylinder was further characterized bv 

 the presence of a peculiar secondary wood. Other points of anatomy need not be 

 considered here. 



Observations on the Genus Equisetum. 



The development of the prothallus of Equisetum has been very elaborately studied 

 by Buchtien (Eiitwick. prothall. von Equisetum), and the writer's investigations accord in 

 their results with his, so far as they have gone. The gametopliyto consists of a median 

 vertically growing fleshy axis terminated by meristematic tissue, in which it is not pos- 

 sible to make out a definite apical cell. From this terminal, actively dividing tissue 

 lateral lobes are produced, to which the sexual organs have a definite relation. The 

 main axis seldom forks in E. Ihaosum and U. arvense, but frequently does so in the large 

 prothalli of £!. hiemale chiefly studied by the writer, and there may be as many as four 

 or five secondary axes in the latter species. 



The antheridia are formed at the tips of the lobes in a manner which has been 

 often described and need not be referred to here. The antherozoids likewise do not 



