Amongst Cycads, Zamia is confined to the New World, and amongst Conifers, Araucaria, limited to the southern hemisphere, has scarcely less antiquity; Pinus reaches as far south as Cuba and Nicaragua.
Xxiv.; Webber, The Development of the Antherozoids of Zamia, Bot.
- Stems tuberous or columnar, not infrequently branched, rarely epiphytic (Peruvian species of Zamia); fronds pinnate, bi-pinnate in the Australian genus Bowenia.
Zamia (South America, Florida, &c.).
- Like Zamia, except that the ends of the stamens are flat, while the apices of the carpels are peltate.
Cases have been recorded (by Thiselton-Dyer in Encephalartos and by Wieland in Zamia) in which the short carpellary cone-scales exhibit a foliaceous form.
Similar spermatozoids were observed in some species of Zamia by H.
In Zamia floridana, the traces are described by Wieland in his recent monograph on American fossil cycads (Carnegie Institution Publications, 1906) as possessing a more direct course similar to that in Mesozoic genera.
(1900); Webber, " Development of the Antherozoids of Zamia," Bot.
In Cycas the altered leaf, upon the margin of which the ovule is produced, and the peltate scales, from which they are pendulous in Zamia, are regarded by all botanists as carpellary leaves.
P. Jaegeri), represented by large pinnate fronds not unlike those of existing species of Zamia, some Equisetaceous plants and numerous Ferns which may be referred to such families as Gleicheniaceae, Dipteridinae and Matonineae.
As examples of these doubtful forms may be mentioned Thinnfeldia, characteristic of Rhaetic and Lower Jurassic rocks; Dichopteris, represented by some exceptionally fine Jurassic specimens, described by Zigno, from Italy; and Ctenis, a genus chiefly from Jurassic beds, founded on pinnate fronds like those of Zamia and other Cycads, with linear pinnae characterized by anastomosing veins.
In a Floridan species of Zamia the leaf-traces are described as characterized by a more direct course from the stele of the stem to the leaves than in most modern genera, thus agreeing more closely with the extinct Bennettites.
In Monoblepliaris, one of the lower Fungi, in some Algae, in the Vascular Cryptograms, in Cycads (Zamia and Cycas), and in Ginkgo, an isolated genus of Gymnosperms, the male cell is a motile spermatozoid with two or more cilia.
In the Characeae, the Vascular Cryptogams, in Zamia and Cycas, and in Ginkgo, the spermatozoids are more or less highly modified cells witi+m.-S, ~..
In the spermatozoids of Chara, Vascular Cryptogams, and in those of Cycas, Zamia and Ginkgo, the cilia arise from a centrosome-like body which is found on one side of the nucleus of the spermatozoid mother-cell.
Even in those cases where the cilia band, which is the product of the centrosome-like body or blepharoplast, enters the ovum, as in Zamia (c in fig.
3); in Encephalartos, Dioon, &c., both rachis and segments are straight; in Zamia the rachis is bent or slightly coiled, bearing straight pinnae.