118 I'n.f. \V. ('. Williamson anl Dr. I). II. Scott. [Feb. 



: 



One important poiiit to be decided was the nature of the canal, 

 which in both genera accompanies each vascular bundle on its inner 

 aide. In Equise.tum these canals, as is well known, mark the posi- 

 tion of the first-formed tracheae of the wood, which have become dis- 

 organised owing to the growth of the surrounding tissues. 



We have now proved that the " intornodal " canals of Calamite* 

 are of precisely the same nature. Here also the canals have been 

 constantly found to contain the annular and spiral tracheae of the 

 protoxylem, which in longitudinal and oblique sections can be re- 

 cognised with perfect distinctness. 



At the nodes the canals are usually interrupted. The primary 

 nodal xylem consists of a girdle of short, often reticulate, tracheae, and 

 closely resembles the corresponding structure in an Equisetum. 



The foliar bundles pass out horizontally at the nodes. Their 

 tracheae are spiral, scalariform, or reticulated. 



In many of the specimens the primary cortex is preserved. Its 

 outer layers are usually more or less sclerotic, and in a few cases 

 alternate hypodermal bands of sclereuchyma and parenchyma can 

 be distinguished, as in many Equiseta. 



On the whole, the primary structure of the stem of Calamitet is 

 substantially that of Equisetum. 



In Calamites, however, secondary tissues were always added, and 

 are only absent from the youngest branches. We have no evidence 

 for the existence of any Calatnite without secondary growth. The 

 process, which went on essentially as in normal Dicotyledons, or 

 Gymnosperms, has been observed at all stages. In the best- 

 preserved specimens the cambium, with the thin-walled phloem 

 outside it, can be recognised. 



The primary medullary rays separating the bundles are in some 

 specimens prolonged, as parenchymatous tissue, through the 

 secondary wood. In the type previously described as Calamopitus 

 the principal rays consist of prosenchymatons cells, and the structure 

 approaches that of Calamodendron. 



In the majority of the typical stems of Calamites (= Arthropitys of 

 Goppert) the principal rays become bridged over by interfascicular 

 wood. In this case most of the radial series of parenchymatous 

 elements die out towards the exterior, and are replaced by series of 

 tracheae. The exact manner in which this change takes place is 

 discussed in the paper. 



The wood consists of tracheae, and of small secondary rays, the 

 cells of which are usually upright. The trachea! elements apj 

 not to be vessels, but tracheides ; they may attain a length of 4 

 The pits, which are bordered, are limited to the radial walls of 

 tracheae, except in the most internal layers of the wood. 



The innermost cells of the primary medullary rays underwent 



