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In Gymnosperms we have seeds, and the carpels may become modified and close around these, as in Pinus, during the process of ripening to form an imitation of a box-like fruit which subsequently opening allows the seeds to escape; but there is never in them the closed ovary investing from the outset the ovules, and ultimately forming the ground-work of the fruit. Germination of Seed.
As we saw, the Primary Era was predominantly the age of Cryptogams; the later periods witness the rise and supremacy of the Phanerogams. But these in turn are broadly divided into a less advanced group, the Gymnosperms, and a more advanced group, the Angiosperms or flowering plants.
The term and its antonym were maintained by Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any approach to its modern scope only became possible after Robert Brown had established in 1827 the existence of truly naked seeds in the Cycadeae and Coniferae, entitling them to be correctly called Gymnosperms.
It is thought by some that the gymnosperms had their station on the drier plains and higher lands. The Carboniferous jungles extended over parts of Europe and of Asia, as well as eastern North America, and reached from the equator to within nine degrees of the north pole. Even in these widely separated regions the genera and species of coal plants are close akin and often identical.
Among the vegetable remains of the Lias, several species of Zamia have been found at Lyme Regis, and the remains of coniferous plants at Whitby. M. Ad. Brongniart enumerates forty-seven liassic acrogens, most of them ferns; and fifty gymnosperms, of which thirty-nine are cycads, and eleven conifers.
As in Gymnosperms, branching is monopodial; dichotomy or the forking of the growing point into two equivalent branches which replace the main stem, is absent both in the case of the stem and the root.
There is no doubt that the phylum of Angiosperms has not sprung from that of Gymnosperms. Within each class the flower-characters as the essential feature of Angiosperms supply the clue to phylogeny, but the uncertainty regarding the construction of the primitive angiospermous flower gives a fundamental point of divergence in attempts to construct progressive sequences of the families.
Reptiles, many and various, gigantic in size, curious in form, some of them recalling the structure of fishes, others anticipating birdlike features, gave a new character to the animal world, while in the vegetable world the reign of the aquatic Cryptogams was over, and terrestrial Cryptogams, and, later, Gymnosperms and Monocotyledonous trees, clothed the earth with foliage.
From that time onwards, so long as these Gymnosperms were, as was usual, reckoned as dicotyledonous flowering plants, the term Angiosperm was used antithetically by botanical writers, but with varying limitation, as a group-name for other dicotyledonous plants.
But we now learn that there is no incompatibility in the co-existence of a vegetation like that of the present globe, and some of the most remarkable forms of the extinct reptiles of the age of gymnosperms.
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