XV] LEPIDOPHLOIOS 105 



Another feature worthy of notice in reference to the leaf- 

 cushions of Lepidodendron is the occurrence in rare instances of 

 alternate zones of larger and smaller cushions. This variation 

 in the size of the leaf-cushions is by no means uncommon in the 

 closely allied germs Sigillaria; in Lepidodendron it has been 

 described by Potonie^ in L. volkmannianum and more recently 

 by Mr Leslie and myself^ in a South African species L. 

 vereenigense. 



Owing to the natural exfoliation of the superficial layers of 

 the outer bark at a certain stage in the growth of the plant, or 

 in some instances no doubt as the result of post-mortem decay, 

 which destroys the delicate cells of the meristematic zone in the 

 outer cortex, isolated leaf-cushions and strips of the external 

 surface are occasionally met with as carbonised impressions. 



The appearance presented by a Lepidodendron stem which 

 has been deprived of its superficial tissues may be dealt with 

 more intelligibly after we have become familiar with the ana- 

 tomical characters. 



iii. Lepidophloios. 



Before proceeding further with the genus Lepidodendron a 

 short account may be intercalated of the external features of a 

 lepidodendroid type of stem which it is customary to describe 

 under a distinct generic title Lepidophloios. This name is con- 

 venient for diagnostic purposes though it seems clear that apart 

 from the form of the leaf-cushion (fig. 146, A) we are at present 

 unable to recognise any well-defined differences between the 

 two forms Lepidodendron and Lepidophloios. For general 

 purposes the name Lepidodendron will be used as including 

 plants possessing leaf-cushions of the type already described as 

 well as those with the Lepidophloios form of cushion. 



The generic name Lepidophloios was first used by Sternberg' 

 for a Carboniferous species which he had previously described 

 as Lepidodendron laricinum. In 1845 Corda^ instituted the 

 name Lomatophloios for specimens possessing the same external 



1 Potoiii6 (05) fig. 4. 2 Seward and Leslie (08) PI. x. figs. 1 and 2. 



3 Sternberg (26) A. PI. xi. figs. 2-4 ; (02) p. 23. 

 ^ Corda (45) A. Pis. i.— iv. 



