. Botany for agricultural students . Botany. STROBILI 447 rangia are produced. The name, however, suggests the likeness of the microsporophylls to the stamens of Flowering Plants. The ovulate strobili are strobili in which only megasporophylls and megasporangia occur. The term ovulate suggests the like- ness of the megasporangium to the ovule of Flowering Plants. The megasporangia are now called ovules because they remain closed, so that the female gametophyte is at no time exposed. It is obvious that the Cycads have carried the differentiation of structures farther than the Selaginellas have.
. Botany for agricultural students . Botany. STROBILI 447 rangia are produced. The name, however, suggests the likeness of the microsporophylls to the stamens of Flowering Plants. The ovulate strobili are strobili in which only megasporophylls and megasporangia occur. The term ovulate suggests the like- ness of the megasporangium to the ovule of Flowering Plants. The megasporangia are now called ovules because they remain closed, so that the female gametophyte is at no time exposed. It is obvious that the Cycads have carried the differentiation of structures farther than the Selaginellas have. In Cycads, not. Fig. 397. — Staminate strobilus and microsporophylls in Cycads. At the left, a staminate strobilus of a Cycad (Dioon); at the right, microsporo- phylls from two different Cycads, showing difference in shape, and the way the sporangia are borne. After Chamberlain and Richard. only spores, sporangia, and sporophylls are differentiated, but there is also a differentiation of strobili. The strobili of Cycads are much larger than those of Selaginella or Lycopodium, and the sporophylls are usually very different from the foliage leaves. In some Cycads the strobili are a foot or more in length and several inches in diameter. In the staminate strobili. the sporophylls are closely crowded and practically have no resemblance to foliage leaves. They vary considerably in shape in different Cycads, but have an outer, expanded, sterile portion and bear the microsporangia, usually grouped in sori, on their under surface (Fig. 397). The ovulate strobili are often much larger than the staminate strobili. The megasporophylls are usually closely crowded, and. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Martin, John N. (John Nathan), b. 1875. New York : John Wiley & Sons, Inc.
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