THE STEM OF CALAMITES 21 



wood has perished, but in a minority the cortex is 

 preserved (see Fig. 4). 



We will defer for the moment the consideration of 

 the wood, which we will take more in detail afterwards, 

 and pass on to the cortex. This consists of two zones, 

 the inner formed of a rather thin-walled tissue, some 

 cells in which contain very dense black carbonaceous 



Fig. 4. — Catamites, sp. Part of transverse section of a young stem, showing pith, 

 cortex, and five vascular bundles, each with a canal at its inner edge. In some of 

 the canals remains of the spiral tracheides can be seen. Beyond the secondary 

 wood, and next the cortex, are traces of the phloem. X about 40. From a photograph 

 by Prof. J. B. Farmer. Will. Coll. 1553. 



matter, and have been supposed to represent secretory 

 organs, while the outer zone consists of smaller cells, 

 with thicker walls. In some exceptional cases we find 

 in this zone regular fibrous ribs alternating with 

 parenchymatous bands. In fact, we have, in such 

 specimens, very much the same mechanical arrangement 

 as we find in the stems of recent Equisetaceae. In a 

 few instances we have been so fortunate as to find stems 



