THE GEOLOGICAL HISTORY OF PLANTS. 



he refers to Calamopitus, has woody bundles com- 

 posed of reticulated or multiporous fibres, with their 

 porous sides parallel to the medullary rays, which are 

 better developed than in the previous form. The inter- 

 vening cellular masses are composed of elongated cells. 

 This is a decided advance in structure, and is of the type 

 of those forms having the most woody and largest stems, 



for 



FIG. 49. Erect Calamites (C. Suckovii), showing the mode of growth of 

 new stems (5), and different forms of the ribs (a, c). (Pictou, Nova 

 Scotia.) Half natural size. 



which Brongniart named Calamodendron (Fig. 50). A 

 third form, to which Dr. Williamson seems to prefer to 

 assign this last name, has the tissue of the woody wedges 

 barred, as in the first, but the medullary rays are better 

 developed than in the second. In this third form the 

 intermediate tissue, or primary medullary rays, is truly 

 fibrous, and with secondary medullary rays traversing it. 

 My own observations lead me to infer that there was a 

 fourth type of calamitean stem, less endowed with woody 

 matter, and having a larger fistulous or cellular cavity 

 than any of those described by Dr. Williamson. 



There is every reason to believe that all these various 





