OVULES AND SEEDS 



Cycads (Fig. IQIB), except that each possessed, in addition to 

 the integument, a second protective covering. This took the 

 form of a lobed cup-like structure (Cu.), 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. 191 A). The 

 robust integument (Fig. IQIB, /.) 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 beyond the micropyle 

 (cf. Fig. IQIA), 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. IQIB, PC.) in 

 which the pollen presumably 

 germinated and liberation of 

 the sperms ensued. The single 

 huge megaspore (m.) has been 

 found filled with a uniform 

 thin-walled prothallus, which 

 doubtless bore the archegonia near its apex. The seed was 

 supplied by a single vascular strand, which gave off branches 

 to both envelopes. Those traversing the cupule (Fig. IQIB, 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 by the method of 'fertilisation and the possession of seeds. 



FIG. 190. Ultimate pinnules of the 

 foliage of Lyginopteris oldhamia, 

 with microsporangia. (From a 

 photograph by Mr. R. Kidston, 

 F.R.S.) 



