398 



NATURE 



[September 21, 191 1 



near the Cycadian end of that chain. Other forms more 

 connected with the Pilicinean phylum oil- still to be 

 sought. 



In bringing Prof. Chodai '- views to your notice, I do not 

 theii tcceptance, but his criticism seems to 



1} weighty to demand a careful reconsideration 



of the structure and affinities of the Lyginodendrea.-, which, 

 whatever may be their ultimate position in our scheme of 

 fication, will continue in the future, as they have done 

 in the past, to command the attention of all botanists 

 interested in the '-volution of plant life. 



If the wholeheartedness with which we in England 

 received the theory of the Cycadian affinity of Lygino- 

 dendron 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 angio- 

 spermous flower," specidation as to the steps by which the 

 evolution 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 

 suggestions connect phylogenetically with the Bennettitales, 

 the Ranales, as primitive Angiosperms, and displace from 

 this position the Amentales and Piperales, which were 

 regarded by Engler as probably more closely related to the 

 Pioangiosperms. 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 know- 

 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 

 Cycadian 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 hypotheses. 

 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 interpretation 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 gynaecium, and not as an 

 inflorescence, we are bound to admit, as do Arber and 

 Parkin, that it is highly modified from the pro-antho- 

 strobilus tvpe 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 amphi- 

 sporangiate Pteridosperms does not seem to me quite 

 justified. Amphisporangiate forms may have been pre- 

 served, or may have arisen anew in various groups of 

 Pteridosperms or in their descendants. Heterospory, we 

 know, originated independently in at least three of the 

 phyla of vascular Cryptogams, and originally, no 

 doubt, the inn strobilus contained both macro- and micro- 

 sporangia, as was the case in Calamostachys Casheana, in 

 trobili of most Lepidodendraceai, and as is still the 

 case in the stmbili of Selaginella .mil in Isoetes. Even in 

 the existing heterosporous Filicineae, micro- and macro- 

 spores are found on the same leaf and on the same sorus ; 

 and though in the higher Cryptogamia and the lower 

 Phanerogamia there may have been a tendency to an 

 iso-sporangiate condition, yet, as the two kinds of spores 

 u 1) homologous in origin, nothing is more natural 

 than an occasional reversion to a heterosporangiate fructifi- 

 cation. Thus, in the group of Gymnosperms, we have 

 many instances of the occurrence of so-railed androgynous 

 cones. In 1801, at the meeting of the British Association 

 at Leeds, I described such amphisporangiate cones which 

 occurred regularly on a Pinus Tkunbergii in the Royal 

 Kew, and only this snring I was able to gather 

 NO. 2l86, VOL. 8/] 



several hermaphrodite cones of Lari.x europea. They havi . 

 of course, been observed and described by many authors 

 for a variety of Gymnosperms. What more likely than 

 that many extinct Gymnosperms may have developed heti n 

 sporangiate fructifications? It is not necessary, therefore, 

 to fix on one group of ancestors for the origin of all 

 existing Angiosperms. Indeed, the great variety of forms, 

 both of vegetative and reproductive organs, which wc 

 meet with in the Angiosperms, not only to-day, but even in 

 the Cretaceous period, in which they first made their 

 appearance, warrants, I think, the belief in a polyphyletic 

 origin of this highest order of plants. It is no doubt trui 

 as Wieland points out, " that the plexus to whii h 

 Cycadoidea belonged, as is the case in every highly 

 organised plant type, presented members of infinite 

 and, indeed, so far as the vegetative organisation goes, we 

 knew already, through the labours of Nathorst, of such a 

 remarkable form as Wielandiella angustifolia, 

 Wieland has shown us a further type in his Mexican 

 Williamsonia. Nevertheless, these diverse forms .all 

 in the structure of their gyntecium, the particular organ 

 which is not so easy to bring into line with that ol 

 Angiosperms. 



I am quite alive to, though somewhat sceptical of, the 

 possibility of a direct descent of the Ranales from the 

 Cycadoidea?, but my hesitation in accepting Arber and 

 Parkin's view of the ancestry of the Angiosperms is 

 enhanced by the consideration that it seems almost more 

 difficult to derive some of the apparently primitive Angio- 

 sperms from the Ranales, than the latter from Cycadoidea. 

 Indeed, this common origin of Angiosperms from the 

 Ranalian plexus will, I feel sure, prove the stumbling- 

 block to any general acceptance of the Arber-Parkin theory. 

 It is easy enough i" assume that all Angiosperms with the 

 unisexual flowers have been derived by degeneration or 

 specialisation from forms with hermaphrodite flowers of the 

 primitive Ranalian type, but unfortunately some of these 

 degenerate forms possess certain characters which appear 

 to me to be undoubtedly primitive. 



It is difficult for those who accept Bower's view of the 

 gradual sterilisation of sporogenous tissue not to regard the 

 many-celled archesporium in the ovules of Casuarina and 

 of the Amentales as a primitive character, and though, as 

 Coulter and Chamberlain point out, this feature is mani- 

 fested by several members of the Ranunculacea? and 

 Rosacea;, as well as by a few isolated Gamopetalae, its 

 very widespread occurrence in the Amentales seems to 

 indicate its more general retention in this group of plants 

 and does not agree readily with the theory that these 

 unisexual orders are highly specialised plants, with much- 

 reduced flowers. The possession of a multicellular arche- 

 sporium is, however, not the only primitive character 

 exhibited by some of the unisexual orders of the 

 Archichlamydeae. Miss Kershaw 1 has shown, in her in- 

 vestigation of the structure and development of the ovule 

 (if Myrica, that in this genus, which possesses a single erect 

 ovule, tin integument is entirely free from the nucellus, 

 and is provided with well-developed vascular bundles, in 

 both of which features it resembles very closely the 

 palaeozoic seed Trigonocarpus. The same features were 

 shown, moreover, by Dr. Benson - and Miss Welsford to. 

 occur in the ovules of Juglans regia, and in a few allied 

 genera, such as Morus and Urtica. Also in a large number 

 of Amentales with anatropous ovules (Quercus, Corylus, 



Castanca, &c), Miss Kershaw has demonstrated the 



rence of a well-di veloped integumentary vascular supply. 



No doubl a furthei search may reveal the occun 



this feature in some other dicotyledonous ovules, but in 



iln in in 1 ns difficult to believe that such a 



primitive vascular system, which tin- \mentales share with 

 the older Gvmnosperms, would have been retained in the 

 catkin-bearing group, if it had undergone far-reaching floral 

 differentiation, ivhil il had disappeared from the plants 

 which in other r spects remained primitive. It would be 

 still mon imagine thai il had arisen in the 



\mentales sub equi ntly to their spe< ialisation. 



There an oth 1 structural characters and general morpho- 

 logical considerations, which I have not time to deal with, 

 which underlie the belief in the primitiveness of the 



1 An ■ ol. xxiii., 1909- " ll,!,i - 



