The Primary Structure of the Stem of Calamites. 1 69 



Not the least perplexing fact about this tissue is that it 

 appears to belong to the cortex, as has been pointed out in 

 the earlier portion of this communication. In some respects 

 it is not unlike a well-developed phloem tissue, and when 

 the older stem was first described by Mr. Cash and myself 

 in 1884, we called attention to this, and tentatively suggested 

 that it might be the phloem of the secondary bundles. 

 Now however that we know it to be a constituent of the 

 cortex of the primary stem, and find it as a broad longi- 

 tudinal band in the leaves, it is clear that this view of its 

 nature can no longer be put forward. In 1876 M. Renault 

 described 1 a form of Calamites \ which he named A rthropitys 

 lineata, in which he found a layer of cortical tissue in which 

 were elements that somewhat resembled those of the layer 

 before us, so far as one can judge in the absence of figures. 

 He speaks of it as a cellular layer, enclosing groups of resin 

 canals, placed in front of the secondary xylem bundles. 

 Solms-Laubach questions this interpretation, 2 but whether 

 true or not for Renault's specimens, it is scarcely applicable 

 to the case before us. For here we have a zone of tissue 

 which is practically uniform and continuous round the 

 whole stem, and not merely a number of isolated "groups" 

 of elements, distinct from, but imbedded in, an ordinary 

 cellular layer. Moreover, the elements of this tissue are 

 themselves mainly cellular, and the carbonaceous masses 

 they contain are apparently derived from the normal cell 

 contents. They might be secretory reservoirs of some kind, 

 but their arrangement as a special tissue is not in favour of 

 this view, and their longitudinal course, both in the stem 

 and the leaves, is more suggestive of the function of con- 

 duction, as already stated. 



Turning to Equisetum, as the living representative of 



1 Comptes rendus, Vol. 83 (1876) p. 574. 

 * Fossil Botany, p. 301, 



