The Present Position of Palaeozoic Botany. 211 



no doubt of the Gj'mnospermous afßnifies of the group under discussion. 

 So far as the seed is concerned, the Pteridosperms were Gymnosperms, 

 on the same level with the Cordaiteae. The only constant peculiarity 

 of the seed is a negative one — the absence of an embryo — and 

 this is common to the Cordaiteae, which in all other respects were 

 as highly organized as recent Gymnosperms. 



If the Pteridospermeae are to be kept distinct it must be on 

 other grounds. The chief characters in question are the following: — 



1. The fact that the seeds were borne on fronds but little 

 modified, as compared with the vegetative foliage. This appears to 

 have been the case in every Pteridosperm where we have any evi- 

 dence on the subject, and affords an important character, though a 

 female Cycas no doubt only differs in degree. 



2. The male organs; like the female, they appear to have 

 been borne on ordinary fronds, and, if we may judge from the one case 

 where they have been investigated, scarcelj^ differed from the sporangia 

 of certain Ferns. Here, so far as the evidence extends, there is a 

 wide difference from any known GA'mnosperms, and a near approach 

 to the Filicineae. 



3. The anatomical Structure. There is probably no con- 

 stant distinctive character in the structure either of stem or leaf. 

 The anatomy of the stem in Lijginodendron does not differ essentially 

 from that in Poroxi/lon, which appears to find its nearest allies in the 

 Cordaiteae, while other plants, such as Pitijs antiqua and Dadoxylon 

 Spenceri (Scott, 1902j which likewise possess primary centripetal 

 wood in the stem, probably also belong to the latter group. It would 

 not always be possible to tell from the structure of the stem alone 

 whether a given plant belonged to the Pteridospermeae or the Cor- 

 daiteae. So too with the leaf — the anatomy of the petiole and 

 lamina in Medidlosa is essentially that of a Cycadophyte, while in 

 Lyginodendron it is that of a Fern. Taking the sum of anatomical 

 characters, however, the Pteridosperms; so far as we know them, 

 are much more Fern-like than any typical Gymnosperm. We might 

 Irame a provisional diagnosis of the Pteridospermeae as follows: 



Male and female sporophylls little differentiated from the 

 vegetative foliage ; no cones formed. Anatomy of either stem, or 

 leaf, or both, of a Filicinean type, as was also the habit. 



The chief practical reason for keeping the Pteridosperms apart from 

 the Gymnosperms is their manifestly more primitive character, shown 

 in one respect or another throughout the group. Even in the seed, 

 the most advanced of their organs, possible primitive indications are 

 not wanting. In Physostoma, with its integument breaking up into a 

 ring of free tentacles taking the place of the micropylar tube, we 



14* 



