SPHENOPHYLLS 213 



different in habit from the Calamite trees. The 

 stem did not exceed a centimetre in diameter, and 

 even that was an unusual thickness. The jointed, 

 ribbed stems bore whorls of leaves commonly 

 six in a whorl at rather long intervals (see fig. 

 24), the leaves of successive whorls being in the 

 same straight line and not alternating; hi this 

 point Sphenophyllum resembled Archceocalamites 

 and differed from the later Calamites and Horse- 

 tails. 



The leaves themselves were often wedge- 

 shaped (the name of the genus means "wedge- 

 leaf"), attached by the thin end and traversed 

 by several forking vascular strands. Sometimes 

 the leaves were deeply cut, and often this went 

 so far that they were completely subdivided to 

 the base, so that the six wedge-shaped leaves were 

 replaced by a larger number of quite narrow seg- 

 ments, each of which appears to be a distinct leaf. 

 Both sorts of foliage often occur on the same plant. 

 Branches were borne at the joints, as in Calamites, 

 and roots also. 



The fructification in some species formed very 

 definite cones, while in others there was little dis- 

 tinction between the fertile leaves and the ordinary 

 foliage. 



The long, slender shoots suggest the idea that 

 the plants may have supported themselves by 

 climbing, like the Bedstraws which scramble over 

 hedges. 



