Fossil plants, Vol. 1 : $b [A text-book] for students of botany and geologySeward, A. C. (Albert Charles)
Science
Fossil plants, Vol. 1 : $b [A text-book] for students of botany and geology
Seward, A. C. (Albert Charles)
Paleobotany
One of the largest examples of _Calamostachys Binneyana_ so far
recorded has a length of 3–4 cm. and a maximum diameter of about 7·5
mm. The axis of the cone bears whorls of sterile leaves or bracts at
equal distances; the linear bracts of each whorl are coherent basally
as a disc or plate of tissue attached at right angles to the central
axis of the cone. The periphery of each of these discs divides up into
twelve linear segments, which curve upwards in a direction more or less
parallel to the strobilus axis, and at right angles to the coherent
portion of each whorl. The manner of occurrence of the whorls is
shown in fig. 94, which has been sketched from a large section in the
Williamson collection. The segments of the successive sterile verticils
alternate with one another, so that in the surface-view of a cone the
long and narrow free bracts appear spirally disposed. Midway between
these alternating sterile verticils there is a series of fertile
appendages, also given off in regular whorls. Each fertile whorl
consists of about half as many members as the segments of a sterile
whorl, and the members of the several fertile whorls are superposed and
not alternate. Each member has the form of a stalk or sporangiophore
given off at right angles from the cone axis; this is expanded distally
into a peltate disc bearing four sporangia attached to its inner face.
In fig. 94 we can only see the basal portions of the sporangiophores,
which are shown in the upper part of the sketch as pointed projections,
_Sp_, from the cone axis. Each sporangiophore is traversed by a
vascular strand which sends off a branch to the base of a sporangium
(fig. 95, A, _t_).
[Illustration: FIG. 94. _Calamostachys Binneyana_ (Carr.) in
longitudinal (radial and tangential) section.
_Sp_, sporangiophores; _S_, sporangia.
(From specimen no. 1022 in the Williamson Collection, British
Museum.)]
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