220 The Palaeontological Record. II Plants 



sprang into being in obedience to a Law of Advance (" Vervollkoni- 

 mungsprincip"), from which other contemporary Lycopods were ex- 

 empt, involves us in unnecessary mysticism. On the other hand it 

 is not difficult to see how these seeds may have arisen, as adaptive 

 structures, under the influence of Natural Selection. The seed-like 

 structure afforded protection to the prothallus, and may have enabled 

 the embryo to be launched on the world in greater security. There 

 was further, as we may suppose, a gain in certainty of fertilisation. 

 As the writer has pointed out elsewhere, the chances against the 

 necessary association of the small male with the large female spores 

 must have been enormously great when the cones were borne high 

 up on tall trees. The same difficulty may have existed in the case 

 of the herbaceous Miadesmia, if, as Miss Benson conjectures, it was 

 an epiphyte. One way of solving the problem was for pollination 

 to take place while the megaspore was still on the parent plant, and 

 this is just what the formation of an ovule or seed was likely to 

 secure. 



The seeds of the Pteridosperms, unlike those of the Lycopod 

 stock, have not yet been found in statu nascendi — in all known 

 cases they were already highly developed organs and far removed 

 from the crytogamic sporangium. But in two respects we find that 

 these seeds, or some of them, had not yet realised their possibilities. 

 In the seed of Lyginodendron and other cases the micropyle, or 

 orifice of the integument, was not the passage through which the 

 pollen entered; the open neck of the pollen-chamber protruded 

 through the micropyle and itself received the pollen. We have met 

 with an analogous case, at a more advanced stage of evolution, in 

 the Bennettiteae (p. 208), where the wall of the gynaecium, though 

 otherwise closed, did not provide a stigma to catch the pollen, but 

 allowed the micropyles of the ovules to protrude and receive the 

 pollen in the old gymnospermous fashion. The integument in the 

 one case and the pistil in the other had not yet assumed all the 

 functions to which the organ ultimately became adapted. Again, 

 no Palaeozoic seed has yet been found to contain an embryo, though 

 the preservation is often good enough for it to have been recognised 

 if present. It is probable 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. 



In these two points, the reception of the pollen by the micropyle 

 and the nursing of the embryo, it appears that many Palaeozoic seeds 

 were imperfect, as compared with the typical seeds of later times. 

 As evolution went on, one function was superadded on another, and 

 it appears impossible to resist the conclusion that the whole differen- 

 tiation of the seed was a process of adaptation, and consequently 



