XI] LEAVES. 409 



afford an example of a form of Sphenophyllum which is repre- 

 sented by such species as S. tenerrimum Ett.^ S. trichomatosmn 

 Stur', and S. myriophyllum^ Crdp. Probably the specimen 

 should be referred to S. trichomatosum, but it is almost 

 impossible to speak with certainty as to the specific value 

 of an isolated leaf-whorl of this form. It has long been known 

 that the leaves of Sphenophylhim may vary considerably, as 

 regards the size of the segments, on the same plant ; and the 

 occurrence of such finely-divided leaves has lent support to 

 an opinion which was formerly held by some writers, that 

 Asterophyllites and Sphenophyllum could not be regarded as well- 

 defined separate genera. This heterophylly of Sphenophyllum 

 has thus been responsible for certain mistaken opinions both as 

 to the relation of the genus to Galamocladus* (Asterophyllites), 

 and as regards the view that the finely-divided laminae belonged 

 to submerged leaf-whorls, while the broader segments were those 

 of floating or subaerial whorls. 



There is a very close resemblance between some of the 

 deeply-cut and linear segments of a Sphenophyllum and the 

 leaves of Calamocladus, but in the former genus the linear 

 segments are found to be connected basally into a narrow 

 common sheath. The assertion* that the deeply-cut leaves occur 

 on the lower portions of stems is not supported by the facts. 

 Kidston' has pointed out that the cones are often borne on 

 branches with such leaves, and the same author refers to a 

 figure by Germar, in which entire and much-divided leaves 

 occur mixed together in the same individual specimen. M. Zeiller 

 recently pointed out to me a similar irregular association of 

 broader and narrower leaf-segments on the same shoots in some 

 large specimens in the Ecole des Mines, Paris. Cones of 

 Sphenophyllum, tenerrimum have been figured by Stur' and 

 others ; they are characterised by their ^mall size and by the 

 dissection of the slender free portions of the narrow bracts^ 



1 Star (75), p. 108. 



2 Stur (87), PI. XV. and Kidston (90), p. 59, PI. i. 



3 ZeiUer (88), PI. lxii. figs. 2—4. 



* Stur (87); Wmiamson (74); Seward (89), etc. 



5 Benault (82), p. 84, and Newbeny (91). ' Kidston (90), p. 62. 



■> Stur (75), p. 114, PI. VII. » ZeiUer (93), p. 32. 



