314 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



that did not form continuous medullary rays. Beyond the normal 

 cambium was the phloem surrounded by internal periderm formed 

 by a phellogen, first in the cortex and subsequently passing inward 

 until it arose in the phloem itself. In Sphenophyllum insigne, a 

 Lower Carboniferous form of Britain and Silesia, the stem was rather 

 larger than the average, although still not over a centimeter in 

 diameter, and differed in having continuous medullary rays, so 

 that the complicated system of vertical and radial parenchyma 

 of the later forms may have been a derived rather than a primitive 

 feature. 



The leaf anatomy presents no unusual characters except its strong 

 mechanical construction, thus precluding the idea advanced by some 

 botanists that the sphenophyllums were aquatic forms. The root 

 anatomy shows no features of special interest. 



At least seven types of cone organization are known, indicating 

 generic differences unsuspected from the external appearance or 

 vegetative habits of the plants. In fructifications of the S. dwwsoni 

 and S. cuneifolium type, the slender cones consisted of a central 

 axis with whorls of proximally connate bracts, the latter with long 

 imbricated pointed tips. Each bract bore two slender — one long and 

 the other short — stalked sporangiophores, so that there were two 

 concentric series to each whorl of bracts. A single pendulous 

 sporangium was borne at the tip of each sporangiophore. The 

 spores were somewhat variable in size, which has been interpreted 

 as indicating incipient heterospory, and appear to have been all of 

 one kind. A second type, described from the Polish Carboniferous 

 as Bowmannites roemeri, had similarly connate whorls of imbricated 

 bracts each of which inclosed three concentric verticils of short- 

 stalked bisporangiate sporangiophores. A third type, S. fertile, had 

 peltate bisporangiate sporangiophores, but was unique in that both 

 the dorsal and ventral lobes were fertile; i. e., the sterile bracts or 

 morphologically dorsal foliar lobes were replaced by sporangia bear- 

 ing fertile lobes. A fourth type, S. majus, had lax cones made up of 

 repeatedly forked bracts each with four sessile or very short stalked 

 sporangia on their upper (morphologically ventral) surface. A fifth 

 type, S. trichomatosum . had a single sporangium near the axis on 

 each bract. In a sixth form, S. marginatum, the sporangiophores 

 were borne on the axis instead of on the bracts. A seventh and re- 

 markably complicated type known as Cheirostrobus is often made the 

 type of a distinct family, the Cheirostrobaceae. It is unfortunately 

 known only from a few petrified cones from the base of the Lower 

 Carboniferous of Scotland. These cones were large, 3 to 4 centi- 

 meters in diameter and about 10 centimeters long, and consisted of 

 closely packed verticils of compound sporophylls, each -of which 

 consisted of three upper (ventral) fertile lobes and three lower 



