LEPIDODENDRON. 351 



ing plants, while their earliest fossil representatives appear 

 to have attained the dimensions of Forest Trees.* 



Existing Lycopodiaceae follow nearly the same law as 

 ferns and Equisetacese, in respect of geographical distribu- 

 tion ; being largest and most abundant in hot and humid 

 situations within the Tropics, especially in small islands. 

 The belief that Lepidodendra were allied to the Lycopo- 

 diaceae, and their size, and abundant occurrence among the 

 fossils of the Coal Formation have led writers on fossil 

 plants to infer that great heat, and moisture, and an insular 

 Position were the conditions, under which the first forms 

 of this family attained that gigantic stature, which they ex- 

 hibit in deposites of the Transition period ; thus corrobo- 

 rating the conclusion they had derived from the Calamites 

 associated with them, as already mentioned.f 



Lindley and Hutton state, that Lepidodendra are, after 

 Calamites, the most abundant class of fossils in the Coal 

 formation of the North of England ; they are sometimes of 

 enormous size, fragments of stems occurring from twenty 

 to forty-five feet long ; in the Jarrow colliery a compressed 

 tree of this class measured four feet two inches in breadth. 



* Prof. Lindley states that the affinities of existing LycopodiaceeE are 

 intermediate between Ferns and ConiferiE on the one hand, and Ferns and 

 Mosses on the otlier ; They are related to Ferns in the want of sexual ap- 

 paratus, and in the abundance of annular ducts contained in their axis ; to 

 Coniferae, in the aspect of the stems of some of the larger kinds; and to 

 Mosses in their whole appearance. 



f The leaves of existing Lycopodiaceae are simple, and arranged in spiral 

 lines around the stem, and impress on its surface scars of rhomboidal or 

 lanceolate form, marked with prints of the insertions of vessels. In the 

 fossil Lepidodendra, we find a large and beautiful variety of similar scars, 

 arranged like scales in spiral order, over the entire surface of the stems. A 

 large division of these are arborescent and dichotomous, and have their 

 branches covered with simple lanceolate leaves. Our figure of Lepidoden- 

 dron Sternbergii (PI. 55. Figs. 1. 2. 3.) represents all these characters in a 

 single Tree from the Coal mines of Swina in Bohemia. 



The form of the scales varies at different parts of the same stem, those 

 nearest the base are elongated in the vertical direction. 



