ON THE STRUCTURE OF THE FRUIT OF CALAMITES. 351 
alternates with the similar whorl above, and in this respect differs from 
V. Ludwigi, in which the leaf- whorls are opposite to each other. The 
apices of the leaves of one verticil pass considerably beyond the united 
bases of those of the superior whorl, and thus form a somewhat closed 
strobilus, enclosing the sporangia. In transverse sections the attenu- 
ated apices are often seen as points between the larger sections of the 
leaf-whorl cut through, as shown in Figs. 3 and 10. 
Between each foliar whorl there is a verticil of leaves, specially de- 
veloped for the support of the sporangia. These leaves have a form 
nearly corresponding to those in the fruit-spike of Equisetum. They 
consist of an orbicular disk somewhat depressed at the centre, where 
the rhomboidal stalk is attached. The margin of the disk is reflexed. 
A-considerable bundle of scalariform vascular tissue proceeds from the 
axis along the stalks. There are six leaves in each whorl, beiug half 
the number of the foliar verticil. Each whorl is opposite to the 
similar ones above and below, and not alternate with them, as in the 
foliar verticils. This is obvious from the longitudinal section repre- 
sented at Fig. 13. The axis has been cut away from the lower half 
of this specimen, and the leaf-stalks are seen cut across, and in a per- 
pendicular series. In V. Ludwigi there are fifteen foliar and five fruit- 
bearing organs, and both series of whorls are respectively opposite to 
the others of the same series. {Vide Journ. of Bot. Vol. IV. Tab. LVI. 
Figs. 7-12.) Ludwig describes the organs supporting the sporangia 
as thorn-like processes. I have, however, repeatedly noticed the sec- 
tion of the peltate apex, and examples may be seen in Figs. 10, 13, 
and 14. Each leaf exhibits two sporangia connected with it in 
transverse (Fig. 9), and the same number in longitudinal section 
(Fig. 13), making four in all. They are borne on the under surface 
of the expanded apex. I have not been able to detect the actual 
connection, but the sporangia are certainly free from the leaf-stalks, 
and the analogy with living organisms leads me to believe that when 
a larger series of specimens are examined, this will be found to be the 
mode of attachment. The wall of the sporangium is composed of 
irregularly elongated cells, with projections of a secondary deposit 
extending at right nudes from the walls into the interior of the cells. 
n "" w o 
(Fig. 4.) The spores are simple globular bodies, frequently exhibiting 
an outer and an inner wall. Sometimes, however, they appear to be 
composed of a single wall, and then the outer wall is represented by 
2 b 2 
