. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. OVULES AND SEEDS ^M Cycads (Fig. 191B), except that each possessed, in addition to the integument, a second protective covering. This took the form of a lobed cup-hke structure {Cii.), comparable with the cupule of a Hazel-nut, and beset with the same glands as occur on the vegetative organs of this plant (cf. Fig. igiA). The robust integument (Fig. 19IB, /.) was fused with the nucellus (sporangium-wall, n.), except for the apical portion, which was pierced by the narrow canal- like micropyle. The tip of the
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. OVULES AND SEEDS ^M Cycads (Fig. 191B), except that each possessed, in addition to the integument, a second protective covering. This took the form of a lobed cup-hke structure {Cii.), comparable with the cupule of a Hazel-nut, and beset with the same glands as occur on the vegetative organs of this plant (cf. Fig. igiA). The robust integument (Fig. 19IB, /.) was fused with the nucellus (sporangium-wall, n.), except for the apical portion, which was pierced by the narrow canal- like micropyle. The tip of the nucellus was produced into a flask- shaped pollen chamber (Pc.), whose neck projected very slightly be3'ond the micropyle (cf. Fig. 191A), so that the microspores reached the nu- cellus direct, a point of con- trast to Cycads and other recent plants. The central portion of the pollen chamber was occupied by a dome of parenchymatous tissue, but between it and the surround- ing wall was a narrow chink- like space (Fig. 191B, Pc.) in which the pollen presumably germinated and liberation of the sperms ensued. The single huge megaspore (in.) has been found filled with a uniform thin-waUed prothallus, which doubtless bore the archegonia near its apex. The seed was â supplied by a single vascular strand, which gave off branches to both envelopes. Those traversing the cupule (Fig. 191B, Vb.) extended into its lobes, whilst those running in the integument () penetrated to the neighbourhood of the micropyle, where the integument became free from the nucellus. The plants described in this chapter are especially charac- terised b}' the method of fertihsation and the possession of Fig 110 âIjltimate pinnules of the foliage of Lyginopteris oldhamia, with microsporangia. (From a photograph by Mr. R. Kidston, ). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illu
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
