X] ANNULARIA. 337 



not find flowers of the rose or tulip; his object being "not to 

 acquire vain glory, but to give occasion for others to look into 

 the matter more clearly." 



The general habit of the fossils which are now included 

 under Annularia agrees closely with that of Calamocladus. 

 There is the same spreading form and a similar foliage in the 

 two genera, but in Annularia the members of a whorl are 

 always fused into a basal sheath, and the segments are not 

 of equal length. We may thus summarise the characteristic 

 features of the genus : — 



Opposite branches are given off in one plane from the nodes 

 of a main axis; the leaves are in the form of narrow sheaths 

 divided into numerous and unequal linear or narrow lanceo- 

 late segments, each with a median vein. The segments in each 

 whorl appear to be spread out in one plane very oblique to the 

 axis of a branch, instead of spreading radially in all directions ; 

 the lateral segments are usually longer than the upper and 

 lower members of a whorl. The vegetative branches possess 

 the same type of structure as Galamites. 



A comparison of Annularia and Fhyllotheca has already 

 been made in Chapter IX. (p. 282). Potoni^^ has recently given 

 a detailed account of Annularian leaves; he compares them 

 with those of Equisetum, and describes the occurrence on the 

 lamina of each leaf-segment of a broad central band or midrib, 

 with a groove, probably containing stomata, on either side. He 

 shows that in well-preserved specimens of Annularia, it is 

 possible to recognise certain minute surface-features, such as 

 the presence of hairs and stomata, which enable one to detect a 

 close resemblance between the leaves of Calamite stems and 

 those of Annularian shoots. 



It is not always easy to distinguish between Annularia and 

 Calamocladus ; the collar-like basal sheath in the leaves of the 

 former is a characteristic feature, but that cannot always be 

 recognised. On the other hand, the leaves of Calamocladus 

 may sometimes be flattened out on the surface of the rock and 

 simulate the deeply cut sheaths of Anmdaria. It is difficult 

 to decide how far the manner of occurrence of Annularian 



1 Potoni^ (93), pp. 169 et seq., PI. xxiv. 



8. •^•> 



