LEPIDODENDRON 161 



tracheae, much larger and more numerous than those 

 of the xylem itself. This peculiar formation appears 

 to have been analogous to the transfusion -tissue in 

 the leaves of Coniferae. In the leaf of Lepidodendron, 

 as in that of the Coniferae, there is some ordinary- 

 parenchyma surrounding the bundle, in addition to the 

 tracheae. 



In the leaves referred to L. Hickii, the structure is 

 much like that just described, except that their form 

 was not acicular, but linear, or narrowly lanceolate, the 

 leaf having a lamina of some width (see Fig. 64). 

 The stomata are extremely well shown (see Fig. 65), 

 and appear to have occupied the same position as in 

 the French species. 



In the structure of the leaves, as in so many other 

 points, we see that the Palaeozoic Lycopods were more 

 highly organised than their representatives in our own 

 period. 



4. Branching. — We now come to the question of 

 the branching of the stem. So far as the external and 

 anatomical characters enable us to judge, the branching 

 was dichotomous throughout, and it is usual to assume 

 that this was the case, though, in the absence of any 

 knowledge of the growing point, it is impossible to say 

 whether the strict definition of dichotomy applied here. 



We must distinguish, with Williamson, between 

 equal and unequal dichotomy. The former prevailed 

 in the forking of the main stem and its principal 

 branches, where the two limbs into which the parent 

 axis divided were similar (Fig. 66). Immediately 

 below the dichotomy the stele separates into two 



