554 TRANSACTIONS OF SECTION K. 



Pteridospermse, Professor Chodat suggests that English palasobotanists have not 

 sufficiently appreciated the work of Bertrand and Corncille 3 on the fibre-vascular 

 system of existing ferns, and have not revised, in the light of the researches 

 of these French investigators, the interpretation given to the arrangement of the 

 primary vascular tissues of Lyginodendron. In Chodat's opinion the structure of 

 the primary groups of wood found in the stem and in the double leaf-trace of this 

 plant is not directly comparable with the arrangement found in the petiole of 

 existing Cycads. In the latter the bulk of the metaxylem is centripetal, while 

 we have in addition a varying amount of small-celled centrifugal wood towards 

 the outside of the protoxylem, and though separated from it by a group of 

 parenchymatous cells, the bundle may be conveniently described as mesarch. In 

 Lyginodendron, and the same applies to Heterangium, the primary bundles of 

 the stem appear- at first sight to be mesarch too, but in Chodat's opinion, if I 

 understand him correctly, the metaxylem is exclusively centrifugal in its develop- 

 ment, but, widening out and bending inwards again, in form of the Greek letter 

 ' a,' the two extremities of the metaxylem are united on the inside of the 

 protoxylem, forming an arrangement described by Bertrand and Corneille in the 

 case of several fern petioles under the name of ' un divergeant ferme.' 



Several details of structure, such as the type of pitting of the metaxylem 

 elements and the separation of the protoxylem from the adaxial elements of 

 metaxylem by parenchymatous cells, confirm Chodat in his view that the primary 

 bundles of Lyginodendron are not really mesarch, and that the stem of Lygino- 

 dendron is essentially Filicinean in nature. Chodat cites other characters, such 

 as the presence of sclerised elements in the pith, and the absence of mucilage 

 ducts, in support of his view of the purely filicinean affinities of the Lyginoden- 

 drese. The presence of secondary thickening in Lyginodendron, he regards not 

 as indicative of Cycadean affinity, but merely as another instance of secondary 

 growth in an extinct Cryptogam, taking up very much the position of Williamson 

 in his earlier controversy with French botanists with regard to the secondary 

 thickening of Calamites and Lepidodendrese. Chodat is also at variance with 

 Kidston and Miss Benson as to the nature of the microspores borne on the 

 fronds of Lyginodendron or Lyginopteris, as he prefers to call this plant. He 

 certainly figures some very fern-like sporangia, attached to the fronds of Lygino- 

 dendron, but anyone who has worked with the very fragmentary and somewhat 

 disorganised material contained in our nodules knows how difficult it is to be 

 absolutely certain of structural continuity. Nevertheless a re-investigation of 

 the whole question of the microsporangia of Lyginodendron seems to me clearly 

 called for by the publication of Chodat's figures. 



As regards the seed-bearing habit of Lyginodendron, Chodat adopts whole- 

 heartedly Oliver's correlation of Lagenostoma with the fronds of Lyginodendron, 

 but would regard the seed, apparently devoid of endosperm at the time of polli- 

 nation, as a somewhat specialised macrosporic development, of more complex 

 structure, but analogous in its nature to the seed-like organ exhibited by 

 Lepidccarpon in another phylum of the Pfceridophyta. ' In any case,' he con- 

 cludes, ' the oi'igin and the biology of this kind of seed must have been very 

 different from those of the seeds of the Gymnosperms. ' 



This contention, based mainly on the tardy development of the endosperm in 

 Lagenostoma, is the least weighty part of Chodat's criticism, for it has never 

 been asserted that the seeds were identical with those of existing Cycads. 

 We know that the seed-habit was adopted by various groups of Vascular Crypto- 

 gams, and it is revealed in fossil plants in various stages of evolution, so that 

 it may be readily presented to us at a special stage of its evolution in Lyginoden- 

 dron. Moreover, we must remember that in so highly organised a Gymnosperm 

 as Pinus, the macrospore itself is not fully developed at the time of pollination. 

 Though not suggesting this as a primitive feature in the case of the pine, we 

 can well imagine how, by a gradual process of 'anticipation,' the prothallus 

 might become established before pollination in any group of primitive seed- 

 bearing plants. There are other more specialised rather than primitive features 

 in the complex structure of Lagenostoma which might with much more reason 



3 Bertrand, C. E., and Corneille, F. : 'Etude sur quelques oaracteristiques 

 de la structure des filicinees actuelles,' Travmix et memoir cs de I'Universitc de- 

 Lille, 1902. 



