204 THE EVOLUTION OF PLANTS 



cells of the latter are in some fortunate cases quite 

 well preserved. Most Calamites are found in 

 this advanced state it is rare to catch the young 

 stem before secondary growth had begun. The 

 presence of the secondary tissues long misled 

 some of the best botanists as to the true nature 

 of these plants. The good old idea of Equisetum- 

 relationship was given up for a time and the Ca- 

 lamites supposed to be Gymnosperms, because it 

 was thought incredible that a Cryptogam should 

 have secondary wood like a Conifer. In fact, the 

 same question arose here as in the case of Sigillaria 

 among the Lycopods (see above, p. 179). In- 

 creased knowledge of the fructifications, together 

 with the analogy of other groups, has settled the 

 question, and secondary growth in Cryptogams 

 is now just as familiar a conception as it is in the 

 case of Seed-plants. 



In Calamites itself, the structure of the wood 

 and bast is just about on a level with that in a 

 Conifer, of course with differences in detail. In 

 other cases, especially Calamodendron, an Upper 

 Coal Measure genus, the complication was greater, 

 the medullary rays being especially elaborate. 

 Some of the Calamites produced a very thick 

 bark, like the Cork Oak. In most of them the 

 course of the vascular strands was like that al- 

 ready mentioned in some of the Triassic Horse- 

 tails; they were more numerous relatively to the 

 leaves than in Equisetum. 



