PRESIDENTIAL ADDRESS. 555 



be invoked, to show that the seed of Lyginodendron does not form a step in the 

 series of forms leading to the Cycadean ovule. 



But leaving this point out of consideration, Chodat brings forward some 

 strong reasons for his conclusions that the Lyginodendrese were plants possess- 

 ing stems of purely fern-like structure, increasing in thickness by means of a 

 cambium, that their foliage was of filicinean structure, but provided with two 

 kinds of sporangia, microsporangia similar to those of Leptosporangiate ferns, 

 and macrosporangia of specialised type, containing a single macrospore. This 

 group, therefore, Chodat regards as a highly specialised group of ferns, which, 

 he considers, shows no particular connection with the Cycads, and which may 

 have formed the end in a series of highly differentiated members of the Filicinew. 



Of the Medullosae, on the other hand, Chodat takes a very different view. 

 Both in the structure of their primary and secondary growth, as well as in 

 their polystely, he sees close affinity of these forms to the Cycads, borne out 

 by smaller secondary features, such as the presence of mucilage ducts, and the 

 simple form of pollen-chamber. Chodat considers the agreement of the Medul- 

 losas with the Cycadaceae to be so close that he regards them as Protocycadese, the 

 fern-like habit being restricted to the position of the sporangia on the vegetative 

 fronds. Medullosa, therefore, would be only one link in the chain connecting 

 the Cycads with the Filicales, and a link very near the Cycadean end of that 

 chain. Other forms more closely connected with the Filicinean phylum are 

 still to be sought. 



In bringing Professor Chodat's views to your notice, I do not wish to urge 

 their acceptance, but his criticism seems to me sufficiently weighty to demand 

 a careful reconsideration of the structure and affinities of the Lyginodendreae, 

 which, whatever may be their ultimate position in our scheme of classification, 

 will continue in the future, as they have done in the past, to command the 

 attention of all botanists interested in the evolution of plant life. 



If the wholeheartedness with which we in England received the theory of 

 the Cycadean affinity of Lyginodendron has laid us open to friendly criticism, 

 I am afraid some of us may be accused of exceeding the speed-limit in our 

 rapid acceptance of the Cycadoidean ancestry of the Angiosperms. Ever since 

 Wieland put forth the suggestion in his elaborate monograph of the ' American 

 Fossil Cycads ' that ' further reduction and specialisation of parts in some such 

 generalised type, like the bisporangiate strobilus of Cycadoidea, could result in 

 a bisexual angiospermous flower,' speculation as to the steps by which the evolu- 

 tion might have been brought about has been rife, and Hallier in Germany 

 and Arber and Parkin in England have put forward definite schemes giving 

 probable lines of descent. Arber and Parkin in their criticism and detailed sug- 

 gestions connect phylogenetically with the Bennettitales, the Eanales, as primi- 

 tive Angiosperms, and displace from this position the Amentales and Piperales, 

 which were regarded by Engler as probably more closely related to the Pro- 

 angiosperms. Of course, the resemblance between the amphisporangiate, or, as 

 I should prefer to call it, the heterosporangiate 'strobilus' of Cycadoidea, and 

 the flower, say, of Magnolia is very striking, and the knowledge we have gained 

 of the structure and organisation of the Bennettitales certainly invites the 

 belief in a possible descent of the Angiosperms from this branch of the great 

 Cycadean plexus ; but the ease with which the flower of the Ranales can in some 

 respects be fitted on to the ' flower ' of Cycadoidea raises suspicion. Critics 

 of the Arber-Parkin hypothesis may possibly incline to the view that ' truth 

 is often stranger than fiction,' and that the real descent of the Angiosperms 

 may have been much less direct than that put forward in these recent hypo- 

 theses. The particular view of the morphology of the intraseminal scales and 

 seed pedicles adopted by Arber and Parkin is, as they admit, not the only inter- 

 pretation that can be put upon these structures, and the views on this point 

 will probably remain as various as are those of the female cone of Pinus. Even 

 if we regard the ovulate portion of the Cycadoidean ' flower ' as a gymecium, and 

 not as an inflorescence, we are bound to admit, as do Arber and Parkin, that 

 it is highly modified from the pro-anthostrobilus type with a series of carpels 

 bearing marginal ovules. Cycadoidea was evidently a highly specialised form, 

 and may well have been the last stage in a series of extinct plants. 



Arber's very sharp separation of mono- and amphisporangiate Pteridosperms 



