HICK : CALAMOSTACHYS BINNEYANA. 
283 
served measures 13 cm. in length, carries 11 " nodal disks," and has 
its axis cut nearly radially throughout its entire length. As here dis- 
played the central tissue is found to be made up of cells which are 
longitudinally elongated, with end walls often but not universally rec- 
tangular, figs. 2, PL I., and 3, PI. II. The cell-walls are for the most part 
thin except at and in the neighbourhood of the " nodal disks" 
where they are thicker, and the cells themselves somewhat shorter. 
In the last quotation from Williamson" it will be noted that the 
central tissue is said to vary very much in different specimens. Some 
variation is shown by the preparations under consideration, but it 
only affects the wall thickenings, the size of the elements, the 
completeness of the tissue, and other minor matters. In no case is 
the center found to be occupied by vascular tissue when cut exactly 
in the radial and longitudinal direction. 
Primary Vascular Bundles. 
Returning to the transverse sections, there is another feature to 
be noticed which is a still more significant one. This consists of 
(usually) three empty spaces in the tissue which abuts on the peri- 
phery of the pith. They vary in size in different specimens, and are 
sometimes irregular at the margin as if the tissue round them had 
been torn. These cavities when well preserved at once recal the 
intercellular passages met with in the primary vascular bundles of 
Equisetum and A rtkropitys, and there can be no doubt that they are 
strictly homologous with them. In other words, they are the carina! 
canals of the primary vascular bundles of the axis, and their presence 
affords positive proof that the bundles are of the Calamitean type. 
Singularly enough, one or more of these canals arc vaguely indicated 
in some of the figures of transverse sections previously published, 
but no one has recognised them as characteristic structures. 
Williamson certainly mentions them in his tenth Memoir,-}- where he 
describes them as " small vacant spaces which doubt- 
less transmitted vascular bundles to the sporangiophores," but he 
failed to identify them as the intercellular canals of imperfect 
bundles, and so missed their significance and homologies. 
* Ante, p. t Op. cit., Pt. x., 1880, p. 503. 
