326 
PROFESSOR W. WILLIAMSON ON THE ORGANIZATION 
terminating some of the upper series, c" , c", indicated by m, appear to be identical 
with those similarly indicated in fig. 25 of my previous memoir on Calamites. It was 
perfectly clear to me when that memoir was written, that though the cellular 
structures, /, appeared to be but modifications of the primary medullary rays through 
which they pass, they nevertheless had some specialised character and function ; and 
that them existence characterised the subgenus Calamopitus which I proposed to 
establish for the reception of the plants which exhibit these peculiar organs. 
Mr. Butterworth’s sections, especially that represented in fig. 24, confirm these 
conclusions. I have already shown that in all Calamites, save very small ones, soon 
after leaving the medulla the primary medullary rays almost entirely disappear. They 
have done so in the present figure, in which their normal position in the upper 
internode is only indicated by the dark lines c, c. This section is also tangential, 
but more peripheral, from the same specimen as that which furnished fig. 23 ; 
but it will be observed that as the exterior of the stem has been much enlarged by 
exogenous growths, all the lenticular organs have also become much larger both in 
length and breadth than is the case in that figure. The remarkable feature revealed 
by this section is, that whilst all the primary medullary rays have disappeared, their 
lenticularly enlarged upper extremities, fig. 23, l, remain as the circumscribed lenti- 
cular areas, l, of fig. 24. These two figures being drawn to the same scale, i.e., 
enlarged 8 diameters, a comparison of the organs, l of fig. 24, with the corresponding 
terminations, l, of the primary medullary rays, c of fig 23, will show how much these 
organs, whatever their functions, have increased in size as they proceeded outwards. 
A radial section shows that they contain no traces of vessels. Fig. 25 represents 
one of these lenticular organs enlarged 25 diameters. The cells of its upper and 
lower extremities are large, like those of the primary medullary ray of which it is a 
remnant, whilst those of its centre are small. Their appearance is much the same in 
the radial section, only in it they are slightly elongated radially, i.e., in the direction 
in which they are proceeding to reach the bark. 
These facts, I think, show that I was perfectly accurate when in my memoir 
Part I., I assigned great importance to these organs. In that memoir I regarded the 
upper and smaller series, m, as supplying leaves or small twigs, believing that they con- 
tained vascular bundles. I am doubtful if I was correct on this point. * I believe that 
the transversely divided structures are chiefly cells, as already stated. In three cases 
I traced the development of the lower series, l, into verticils of the radiating infranodal 
canals, illustrated by fig. 31, which represents the lower extremity of the sandstone 
cast of the medullary cavity of a Calamite surrounded by the disorganised carbon, f f, 
of its vascular zone. The radiating spokes, l , are also sandstone casts of the interiors 
* Since this was written I Lave studied a vertical radial section of a Calamite sent to me by Mr. Binns, 
of Halifax, in wbicb some of the vessels ascending from below are, on reaching one of these lenticular 
organs, conspicuously deflected outwards, making it clear that some vessels do accompany these cellular 
radii in their outward course, confirming my original conclusion. 
