CYCADOFILICALES 47 



testa, may occur at any stage; and if the testa is formed before fertili- 

 zation (as may have been true in paleozoic seeds), the growth of the 

 embryo may well have been checked at some stage of the proembryo, 

 in which case there would be no recognizable embryo. That even 

 a well-organized testa does not check the growth of the embryo, 

 however, is evidenced by the fact that even among existing gymno- 

 sperms, as cycads, the true embryo (as distinct from an extensive 

 proembryo) may escape from the seed as soon as it is developed and 

 grow as continuously as do the embryos of pteridophytes. In such 

 a case, however, the chance of finding preserved a recognizable embryo 

 invested by the testa would be as exceptional as of finding any very 

 brief stage in the life history. It would seem, therefore, that in paleo- 

 zoic seeds there was either no resting period between intraseminal 

 and extraseminal development of the very young plant, or it occurred 

 in the proembryonic stages. Scott (86) has suggested as " 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." 



Since belief in the absence of embryos from paleozoic seeds rests 

 as yet upon negative evidence, it should not be forgotten that the 

 sections of suitably preserved seeds are far too few in number to over- 

 come the uncertainty of negative evidence or the possibility of abortive 

 seeds. In fact, comparatively few seeds have been found attached 

 to the shoots that bore them, and seeds that have fallen off at the 

 immature stages suggested by all published figures of sections would 

 be abortive seeds, so far as experience with living seed plants is con- 

 cerned. Only good seeds remain on the plant, and there is no record 

 of a section of an attached paleozoic seed. Moreover, if the seeds 

 germinated at once, as do those of the cycads, no embryos would 

 be found except in attached seeds. The seeds of Bennettitales that 

 show conspicuous embryos are all attached seeds, and it is altogether 

 probable that such seeds of Cycadofilicales and of Cordaitales will 

 also show embryos. 



Scott (28) has described a seedlike megasporangium {Lepido- 

 carpon) belonging to the lycopods of the Lower Coal-measures, which 

 may well represent a primitive seed condition. These detached 

 megasporangia had already been described as seeds, but their occur- 



