RELATIONS OF CALAMODENDRON TO CALAMITES. 267 



to be barred, as we have seen to be the case with those of 

 ordinary Calamites ; the medullary rays_, I', consisting of 

 parenchymatous cells_, are as conspicuous here as they are 

 in the transverse section. This greater development of these 

 secondary medullary rays distinguishes Calamodendron 

 striatum from ordinary Calamites, but this cannot be 

 regarded as a generic feature, much less as an ordinal one- 



On each side of this vascular wedge we have the two 

 radial zones g, g, corresponding to the primary medullary 

 rays of figures 4 and 5. The transverse section shows 

 these rays to be composed of cells whose diameter is 

 very much smaller than that of the vessels composing the 

 vascular wedge on each side of which they are grouped. 

 Their appearance in this section closely corresponds with 

 that of a Coniferous wood. Turning to their longitudinal 

 and tangential sections, g' , g\ we find that these cells are 

 prosenchymatous and partially sclerenchymatous. They 

 are long fibrous structures such as we find abundantly in 

 many Equisetiform and other Cryptogamic plants. In 

 the transverse section, g, we see some parenchymatous 

 medullary rays, as at g\ g', and at g" , g", in the tangential 

 surface, we see vertical prolongations of these rays as 

 described by Brongniart (see page 257). These have a len- 

 ticular vertical section, and those near the centre of the 

 fibrous zone are unquestionably longer and broader than 

 those in its more lateral portions ; but these central ones 

 are far from being continuous though the internode, as they 

 are described by Brongniart. 



In my transverse sections of Calamodendron striatum the 

 radial length of what I call the primary medullary rays 

 (fig. 6, g) is much greater than is common amongst Cala- 

 mites. In the latter plants these rays generally diminish 

 rapidly in diameter as they proceed outwards, and their ulti- 

 mate external prolongations become, in the most matured 



