60 PTERIDOSPERMEAE [CH. 



is clearly seen: its surface-layer consists of small cells succeeded 

 by a broad band of radially elongated elements closely resembling 

 the alveoli in the prothalli of some recent Gymnosperms, parti- 

 cularly certain Conifers. No archegonia have been discovered. 

 The cupular envelope of immature seeds, compared by Oliver 

 and Scott with the lobed and glandular husk of Corylus colurna 

 L. 1 , receives several vascular bundles of collateral and mesarch 

 structure from the axial strand, and these subdivide as they 

 ascend. The glands which occur on all parts of the cupule are 

 sessile or stalked and identical with those on the vegetative organs 

 of Lyginopteris. Assuming that pollination occurred at a com- 

 paratively early stage in the development of the seed when the 

 cupule was still intact, it is conceivable, as Sir Joseph Hooker 

 suggested, that the glandular secretion may have attracted insects 

 and so aided in the transport of pollen which were perhaps drawn 

 down the narrow pollen-chamber by exuded mucilage as in recent 

 Conifers. The evidence obtained in recent years in favour of 

 insect-pollination in certain Cycads and in Welwitschia lends 

 support to this view: the dragon flies hovering over a fertile 

 Lyginopteris frond in a recent restoration 2 may be a legitimate 

 addition. 



A striking feature of Lagenostoma as of other Palaeozoic 

 seeds is the absence of an embryo : this and other considerations 

 have led certain authors, notably Chodat 3 , to question the justi- 

 fication for the use of the term seed. Various suggestions have 

 been offered in explanation of this fact. In recent Cycads, as 

 already pointed out, the development of the embryo does not 

 always occur before seed-fall. It may be that these older seeds 

 had no resting-period or there may have been a period of rest 

 after fertilisation and not as now at a stage subsequent to the 

 formation of the embryo 4 ; it is also suggested by Scott that 

 ' the nursing of the embryo had not yet come to be one of the 

 functions of the seed, and that the whole embryonic development 

 was relegated to the germination stage 5 .' In this connexion 



1 For figure, see Lotsy (09) p. 714. 



2 Scott (11) p. 105. 



3 Chodat (08) B. * Scott ( 03) 



5 Scott (09) B. p. 220. See also Oliver (05); Oliver and Scott (04) p. 231. 



