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 

 ■ 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 

 (I.b.) 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 seeds. 



Fig 1 10 — Ijltimate pinnules of the 

 foliage of Lyginopteris oldhamia, 

 with microsporangia. (From a 

 photograph by Mr. R. Kidston, 

 F.R.S.) 



