Abnormal specimens of Equisetum in which the strobilus is interrupted by whorls of leaves are of interest for comparison with the fructification of Phyllotheca.
This similarity is closest in Archaeocalamites, an ancient type found in Upper Devonian rocks; in this the strobilus consists of peltate sporangiophores inserted in whorls on the axis.
A lengthening of the axis of the female strobilus of Coniferae is not of infrequent occurrence in Cryptomeria japonica, larch (Larix europaea), &c., and this is usually associated with a leaf-like condition of the bracts, and sometimes even with the development of leaf-bearing shoots in place of the scales.
14), or branching as in palms. A spike bearing female flowers only, and covered with scales, is a strobilus, as in the hop. In grasses FIG.
(Spadix) Arum, some Palms. (Strobilus), Hop.
C. Casheana, Will., two kinds of spore occur, in different sporangia, but on the same strobilus and even on the same sporangiophore.
This form of strobilus, from the Coal Measures of Germany, is imperfectly known, and its relation to Calamarieae not beyond doubt.
In the peduncle of the strobilus secondary tissues are formed.
In the cone attributed to the Lower Carboniferous Lepidodendron Veltheimianum) the arrangement was that usual in Selaginella, the microsporangia occurring above and the megasporangia below in the same strobilus (diagram, fig.
In Selaginellites Suissei there was a definite strobilus bearing both microand megasporangia; in each of the latter from 16 to 24 megaspores were contained; in Selaginellites primaevus, however, the number of megaspores was only 4, and the resemblance to a recent Selaginella was thus complete.
Selaginellites elongatus, another heterosporous species, is remarkable for having no differentiated strobilus, a condition not known in the recent genus.