CALAMARIEAE. 341 



Dresden, figured and discussed by Petzholdt J and Geinitz 2 , may be cited 

 in proof of this. Petzholdt's Calamitae are imbedded in grayish white 

 Carboniferous sandstone, and show on the transverse section a central 

 space filled with the stone, and surrounded by a rather thick compact 

 envelope of coal. But this layer of coal, itself with a rather irregular 

 outline on the outside and on the inside and with many small projecting 

 teeth, is cut up by a circle of lacunae filled with the stony matter into 

 segments which have the shape of the transverse section of a double "[". I 

 have myself seen several sections of the kind in Dresden and Strassburg 

 from Petzholdt himself, and they appear in his tables well-drawn and true 

 to nature. Now he has explained the whole of this structure by the 

 direct unaltered preservation of the original state of the stems, and Schimper 3 

 and others have adopted this view. The lacunae therefore in the rind 

 of coal were the vallecular canals, the central space the medullary cavity 

 of the Equisetum-like stem. Still the irregular nature of the layer of coal 

 must cause some hesitation, and its thickness must seem surprising, if we 

 hold to the view that it was produced from the wall of a herbaceous 

 hollow stem. And in fact Schenk 4 , who has submitted these remains 

 to fresh examination, has succeeded in proving that the mass of coal in 

 it consists entirely of secondary wood, which was torn and broken up 

 only in the process of imbedding ; that the lacunae are thus in the 

 middle of the wood and only represent defective places in it, and that 

 they therefore cannot be compared with the vallecular canals. The 

 specimens are in fact remains of Calamodendron or mixed masses of 

 Calamodendron and Psaronius, which are not in question as regards our 

 argument. 



The view of Brongniart and his pupils is founded in the main on the 

 petitio principii which will not hear of secondary growth in Archegoniatae. 

 But it appears to me that the facts as observed in Lepidodendron and 

 Sigillaria, and even in the recent Isoetes, leave so little foundation for this 

 idea, that it can no longer be employed as a main argument. The 

 points brought forward in support of it, where they have not been already 

 disposed of, are of little value. Much importance is attributed for 

 instance to the difference in the thickness of the rind of coal. But thin 

 coverings of coal are formed even when there is only a small amount 

 of secondary growth, and we discover how greatly the amount varied 

 by examining large collections of sections. No one of the many dif- 

 ferences which Grand' Eury ascertained in the underground organs of 

 our plants is of such a kind as to imply more than a generic, or shall 



1 Petzholdt (1). a Geinitz (5). 3 Schimper (1), vol. i. 4 Schenk (2), 



p. 236. 



