340 Br. B. H. Scott [May 15, 



our hot-houses Cycads are seldom fertilised ; yet the conspicuous 

 scarlet seeds of Cycas revoluta or the crimson seeds of Encephdlartos 

 are familiar objects to many Kew visitors. Further, the degree of 

 development of the embryo at the time the seed is shed is very in- 

 constant ; sometimes, although fertilisation has taken place, the 

 embryo is scarcely to be detected. 



The definite resting stage of the young plant in the dry seed, so 

 characteristic of the higher Phanerogams, is unknown to these 

 primitive seed-bearers, the Cycads and the Maidenhair-tree, and the 

 same appears to hold good for the seeds found in the Palaeozoic rocks. 

 Such seeds are common in certain localities, as in the Coal Measures 

 of Central France, and to a less degree in our own coal-beds. In 

 petrified specimens the structure is often beautifully preserved, yet 

 in no single case has a Palaeozoic seed been found to contain an 

 embryo. It is not merely a matter of preservation, for that is not 

 unfrequently so good that the delicate egg-cells can still be recognised. 

 Thus there is no " seed " of Palaeozoic age, which, according to 

 current definitions, strictly deserves the name. Technically, the 

 term " ovule " would be more appropriate, but the obvious maturity 

 of the integument makes the word " seed " seem more natural. So 

 far the case is parallel to that of our recent Cycads or Maidenhair- 

 tree. 



It is of course possible that any day we may light on some 

 Palaeozoic seed with an embryo ; it may be that the specimens 

 hitherto found were all unfertilised, though the frequent presence of 

 pollen-grains in the pollen-chamber makes this explanation unlikely. 

 It seems not improbable that the development of an embryo in the 

 ripening seed was a later device ; that in the older seed-plants the 

 period of rest came immediately after fertilisation, and that the 

 growth of the embryo, when once started, went on rapidly and con- 

 tinuously to germination. In that case a seed with a recognisable 

 embryo would rarely be preserved. 



We are now in a position to see what are the chief advantages 

 gained by a plant in adopting the seed habit, they are : — 



1. Pollination on the parent plant, and consequently greater 

 certainty in bringing together the two kinds of spore. 



2. Fertilisation either on the plant, or at least within the spore- 

 sac, giving greater certainty of success, and protection at a critical 

 moment. 



3. Protection of the young prothallus from external dangers. 



4. A secure water-supply during its growth. 



5. Similar protective and nutritive advantages for the young 

 plant developed from the egg-cell. This last end, however, was 

 very probably not yet fully attained in the earlier seed-bearing 

 plants. 



We may now go on to consider our main subject for this evening, 

 — the historical question. From what group of spore-bearing plants 

 were the Seed-plants derived ? 



