. A textbook of botany for colleges and universities ... Botany. Fig. - Seeds of Aneimites (an American form). â After White. lamina had disappeared and only the prominent ribs persisted. In some cases, however, the seeds replace sori on ordinary fernlike leaves (fig. 422). There are very many detached paleozoic seeds which have never been connected with the plants that produced them; but doubt- less many of them belonged to the Cycadofilicales. So far as these attached and detached seeds have been sectioned, they show certain features in common which are regarded as primi- tive. In seed
. A textbook of botany for colleges and universities ... Botany. Fig. - Seeds of Aneimites (an American form). â After White. lamina had disappeared and only the prominent ribs persisted. In some cases, however, the seeds replace sori on ordinary fernlike leaves (fig. 422). There are very many detached paleozoic seeds which have never been connected with the plants that produced them; but doubt- less many of them belonged to the Cycadofilicales. So far as these attached and detached seeds have been sectioned, they show certain features in common which are regarded as primi- tive. In seed plants the mega- sporangium has long been called an ovtde. In general structure it consists of a central region (the real sporangium) called the nucellus, which is invested by one or two coats called integu- ments. A passageway (micropyle) is left through the integument at the tip of the nucellus. When the changes occur that transform the ovule into the seed, the integument develops in various ways to form the seed coat or testa. In fossil seeds it is evident that the structure of the ovule must be inferred from the structure of the seed. In the seeds of Cycadofilicales there is a three-layered testa, which is often peculiarly free from the nucellus. The vascular strand that enters the seed divides into two sets of branches, one set traversing the testa, and the other traversing the outer region of the nucellus, in case the testa and nucellus are free. The nucellus is beaked, and contains a deep chamber (pollen chamber), which serves as a gathering place for microspores, and which in living gymnosperms is associated with swimming sperms. A remarkable feature of the seed, and of all paleozoic seeds that have been sectioned, is that there is no trace of an embryo. Since the embryo is present in mesozoic seeds, its absence from paleozoic seeds must be due to other causes than failure to be preserved. Stamens.âThe microsporangiate structures (stamens), first recog- nized in 1905
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