208 THE EVOLUTION OF PLANTS 



In another type of Calamitean cone, the fertile 

 scales, instead of standing midway between the 

 whorls of bracts, sprang from the axil of the bracts 

 below them. This is one of the facts which has 

 suggested a doubt whether the fertile scales were 

 really leaves (sporophylls) or not. It is not very 

 likely that they were branches, but it is quite pos- 

 sible that in both the fructifications in question 

 the scales may have originally been outgrowths 

 from the bracts next below them, and may thus 

 represent parts of leaves, and not entire leaves. 



What has been said so far applies to the Coal 

 Measure Calamites, that is to say, to the forms 

 belonging to the later part of the Carboniferous 

 epoch. We do not know so much about the Cala- 

 mites of the Lower Carboniferous and Devonian, 

 but there are one or two points of interest. The 

 most important of these earlier Calamites is the 

 genus Archceocalamites, from Upper Devonian and 

 Lower Carboniferous strata. This plant, which 

 like its successors was a tree, had several peculiar 

 features. The leaves of successive whorls were 

 placed directly above each other, in the same 

 straight line, whereas in the later Calamites and 

 Horsetails, the leaves of each whorl are alternate 

 with those of the next. A more striking differ- 

 ence is in the leaves themselves, which in Archceo- 

 calamites were long and repeatedly forked, in 

 most marked contrast to the simple little leaves 



