54 
PEOEESSOE W. C. WILLIAMSON ON THE OEGANIZATION 
attached to the stems supporting the strobili. But, unfortunately, in no one of these 
cases is any thing known of the internal organization of the strobili. The only recorded 
examples in which such organization is preserved are Mr. Binney’s Calamostachys 
Binneyana , my Calamitean strobilus, and the Volkmannia Dawsoni, also described by 
myself. In my memoir on Calamites, published in vol. clxi. of the ‘ Philosophical 
Transactions,’ and forming the first part of the present series, I discussed briefly the 
probable affinities of these three fruits (p. 501) ; and in the subsequent memoir on 
Volkmannia Dawsoni , I again examined their respective claims. Since that memoir 
appeared, I have investigated a very considerable number of specimens, all of which have 
tended to confirm the conclusions at which I previously arrived, viz. that the only British 
strobilus , of which the internal organization has hitherto been described , that has any 
claims to be regarded as the fruit of Calamites , is that which I figured in the fourth 
volume of the ‘ Transactions of the Manchester Literary and Philosophical Society .’ 
Such being my conviction, I may exclude this plant from further detailed consideration 
at the present time, and inquire what light my more recent investigations have thrown 
upon the two remaining ones. 
With this aim I have given, in Plate V. fig. 28, a transverse section of the Volk- 
mannia Dawsoni just referred to, but from a section not figured in my previous 
memoir. In order to comprehend this figure, it is necessary to understand that this 
fruit is a strobilus, giving off lenticular bractigerous disks from each node, whilst the 
intervening spaces, corresponding with the internodes, are occupied by successive layers 
of sporangia, each layer consisting of four concentric verticils and occupying a single 
internode. Since the bracts fringing the margin of each nodal disk curve up- 
wards and outwards, the transverse section, which has crossed the fruit somewhat 
obliquely, has cut through the sporangia belonging to two such internodes: those 
marked u belong to two verticils of the inner and upper series, and those indicated by 
u! form a small portion of the peripheral part of the next inferior internodal series, 
ascending to the level of the central portions of the one above it, as it extended 
upwards and outwards ; c indicates the central vascular axis, surrounded by a vacant 
space originally occupied by cellular tissue, of which the only traces now found are 
some of their innermost portions (g), which evidently constitute a thin inner series of 
cells closely investing the vascular bundle, but which have shrunk away from it through 
desiccation, and now adhere only to its angles. The part of the inner circle marked 
k is a transverse section of the outer bark at one of the internodes. On the uppet 
side of the same circle this cylinder of bark appears to be much thickened, because 
the slightly oblique section has here passed through one of the nodal disks. Being so 
near the central axis, we here see no trace of the division of that disk into its peripheral 
verticil of bracts ; but this is clearly seen at t, t', which letters indicate the margin of 
the next inferior nodal disk which ascends as it is extended centrifugally. At t' we can 
trace the first division of this disk into separate bracts, the base of each of which here 
exhibits an almost square section, but with a slight central projection on the outside, 
