124: 



THE GEOLOGICAL HISTORY OF PLANTR 



he refere to Calamoju'tus, has woody bundles com- 

 posed of reticulated or niultiporous tibres, with their 

 porous sides pai-allcl to tlio mcdullai-y iiiys, which are 

 better developed than in the previous form. The inter- 

 vening cellular masses lu-e 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, 



to 



^ 



Fm. 49.— Eroot Oi/umi/K.* {C. Suekovii), showing the mode of growth of 

 now stems (/)), and diftferont forms of the ribs (a, o). (Piotou, Nova 

 Sootla.) lliilf 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 

 bai-red, as in the first, but the medullary rays are better 

 developed than in the second. In this third form the 

 intermediate tissue, or primary moduUury rays, is truly 

 fibrous, and with secondary medullary rays traversing it. 

 My own observations lead mo to infer that there was a 

 fourth type of calamitean stem, loss 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 



