LYGINODENDRON 393 



further evidence came in, to the establishment of the 

 new class Pteridospermeae. 



The seed is, as we have seen, a complex one, and 

 already far removed from the Cryptogamic megaspor- 

 angium ; there is indeed little trace of anything primitive 

 in Lagenostoma beyond the fact that the reception of 

 the pollen was still left to the nucellus — the sporangial 

 part of the seed — and not yet assumed by the integu- 

 ment. The absence of any trace of an embryo is a 

 negative character common to all known Palaeozoic 

 seeds, though there are many instances of the preservation 

 of archegonia (see, for example, Fig. 198, p. 549). Yet 

 the seeds, as a rule, are evidently mature and not mere 

 ovules. Neither, considering the frequent presence of 

 pollen-grains in the pollen-chamber, can we assume that 

 all the seeds found happened to be barren. It is 

 possible that, though pollinated, they were not yet 

 fertilised, the latter process taking place an appreciable 

 time after the seed was shed ; or again, it may be that 

 a resting stage followed immediately on fertilisation 

 before any marked development of the embryo had 

 taken place. In any case it appears that in these 

 ancient seeds the period of rest came much earlier with ( 

 reference to the growth of the embryo than in most of 

 our recent seeds. 1 We find a relic of the old conditions 

 in living Cycads, in which the embryo is often scarcely 

 to be recognised when the seed is ripe and ready for 

 sowing. 



Returning to the seed of Lyginodendron, we have 

 seen that the structure of the pedicel shows that the 



1 It is interesting to see that the Mesozoic Bennettites was completely 

 modern in this respect, for there the embryo was far advanced, and filled 

 the whole embryo-sac before the seed was shed (see Fig. 205, p. 574). 



