The Carboniferous Arborescent Lepidodendra. 55 



inclosed fewer difficulties than my own had done, many 

 serious ones remained. They involved the admission that 

 in their earliest state these young plants were of sufficient 

 magnitude to contain in their interiors a primary trachaeal 

 xylem large enough to contain 6900 individual tracheids, 

 enclosing within their cylinder a medulla of considerable 

 dimensions. How any embryonic growth could attain to 

 such a size is difficult to understand. Of course this question 

 involves the larger one of the primary origin of the young 

 Lepidodendroid plants. 



The only reproductive organs found upon these Car- 

 boniferous Lycopods are either homosporous or heterosporous 

 strobili. This fact at once suggests that, like their living 

 representatives, these plants were primarily sporophytes 

 developed upon a prothallus. The spores produced within 

 the sporangia of these strobili exist in a fossil state in such 

 extraordinary profusion, and continued to be so during such 

 a prolonged epoch, as to make it impossible to suppose 

 that they were produced in vain. In addition to the vast 

 numbers of them still retained within the sporangia of the 

 fossil strobili, we find that they were shed and preserved in 

 the vegetable soil, subsequently converted into coal, in the 

 greatest profusion. A considerable number of the thick 

 coal-seams of Europe, America, and Australia are largely 

 composed of them ; and to suppose that such a provision 

 should be made for the reproduction of the species, and yet 

 be entirely in vain, exceeds all credibility. There seems to 

 be no reason for doubting that the functions of these spores 

 were identical with those of their living representatives, and 

 that those functions were similarly performed. 



Assuming, therefore, that the earliest state of a Lepido- 

 dendron was that of a minute sporophyte, other questions 

 arise. One of these has reference to the existence of a 

 primary root. Were the remarkable organs now known 

 as Stigmarise the first to fulfil the functions of roots to these 



