1 86 Mr. Thomas Hicks on the 



interesting form. At h, we see the " fascicular " * canal, en- 

 larged somewhat by the destruction of the peripheral 

 elements, and at x, two protoxylem elements projecting 

 into it. Here, then, we have a vascular bundle of the true 

 Calamitean type, and a confirmation of the conclusion that 

 the leaves under consideration are the leaves of Calamites. 



Besides these and other less pronounced differences in 

 the form of the transverse section, certain differences of 

 structure are also met with. In the two sections last dealt 

 with both the " melasmatic " and the assimilating tissues are 

 continuous, but in that of Fig. 4 the former appears to be 

 interrupted at the middle point on the upper side by an 

 element which is probably sclerenchymatous. In Fig. 7, 

 taken from a preparation for which I am indebted to 

 Mr. Binns, we have a case where the interruption is greater, 

 and extends to the assimilating tissue also. In other words, 

 we see the assimilating and the "melasmatic" tissues 

 thinning out towards the middle line of the upper surface 

 of the leaf, where they are replaced by elements of a 

 different kind. A comparison of this and similar sections 

 with fragments of longitudinal sections, teaches that these 

 elements are sclerenchymatous and, where they are present, 

 they form a strand which runs beneath the epidermis along 

 the middle line of the upper surface of the leaf. 



It is an interesting question whether these differences 

 are due to hetrophylly or to the fact that the sections 

 are taken at different points along the length of the 

 leaf. With some reservation I adopt the latter view 

 as more in accordance with observed facts, and am 

 disposed to regard the sections shown in Figs. 5 and 6 as 

 taken near the base of the leaf, that of Fig. 4 as taken at 

 some distance from the base, and that of Fig. 7 as taken 

 nearer the tip. As to this last, there is little doubt that 



* In using this very convenient term I follow the example set by Prof. 

 Williamson and Dr. Scott. Phil. Trans., 1894, p. 870. 



