286 PTERIDOPHYTA. [CH. 



described by Schmalhausen in which a branch bears clusters 

 of sporangiophores, alternating with verticils of sterile bracts. 

 The sporangiophores appear to have the form of stalked peltate 

 appendages bearing sporangia, very similar to the sporangio- 

 phores of Bquisetum. Solms-Laubach^ has examined the best of 

 Schmalhausen's specimens, and a carefully drawn figure of one 

 of the fertile branches is given in his Fossil Botany. 

 ' The significance of this manner of occurrence of sporangio- 

 phores and whorls of sterile bracts on the fertile branch will 

 be better understood after a description of the strobilus of 

 Calamites. In Phyllotheca the sporangiophores appear to have 

 been given off in whorls, which were separated from one another 

 by whorls of sterile bracts, whereas in Equisetum there are no 

 sterile appendages associated with the sporangiophores of the 

 strobilus, with the exception of the annulus at the base of the 

 cone. Heer^ first drew attention to the fact that in Phyllotheca 

 we have a form of strobilus or fertile shoot to a certain extent 

 intermediate in character between Equisetum and Calamites. 



In abnormal fertile shoots of Equisetum, sporophylls occa- 

 sionally occur above and below a sterile leaf-sheath. Potoni^^ 

 has figured such an example in which an apical strobilus is 

 succeeded at a lower level by a sterile leaf-sheath, and this again 

 by a second cluster of sporophylls. As Potonie points out, this 

 alternation of fertile and sterile members affords an interesting- 

 resemblance between Phyllotheca and Equisetum. It suggests 

 a partial reversion towards the Calamitean type of strobilus. 



2. Phyllotheca Brongniarti Zigno. Fig. 68, A. 



This species of Phyllotheca from the Lower Oolite rocks of 

 Italy is known only in the form of sterile branches. The leaves 

 are fused basally into an open cup-like sheath which is dissected 

 into several spreading and incurved linear segments. The 

 internodes are striated longitudinally ; they are about 2 mm. 

 in diameter and 10 mm. in length. 



1 Solms-Laubach (91) p. 181, fig. 17. 



2 Heer (82) p. 9. 



3 Potonie (962) p. 115^ fig^ 3. 



