470 



SCIENCE 



[N. S. Vol. XXXIV. No. 876 



Williamson in his earlier controversy with 

 French botanists with regard to the sec- 

 ondary thickening of Calamites and Lepi- 

 dodendrea;. 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 cer- 

 tainly figures some very fern-like spo- 

 rangia, attached to the fronds of Lygino- 

 dendron, but any one who has worked with 

 the very fragmentary and somewhat dis- 

 organized material contained in our nod- 

 ules knows how difficult it is to be abso- 

 lutely certain of structural continuity. 

 Neverthless, a reinvestigation of the whole 

 question of the microsporangia of Lygino- 

 dendron 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 Lageno- 

 stoma with the fronds of Lyginodendron, 

 but would regard the seed, apparently de- 

 void of endosperm at the time of pollina- 

 tion, as a somewhat specialized macrosporie 

 development, of more complex structure, 

 biit analogous in its nature to the seed-like 

 organ exhibited by Lepidocarpon in an- 

 other phylum of the Pteridophyta. "In 

 any case," he concludes, "the origin 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 Cryptogams, and it is 

 revealed in fossil plants in various stages 

 of evolution, so that it may be readily pre- 

 sented to us at a special stage of its evolu- 



tion in Lyginodendron. Moreover, we 

 must remember that in so highly organized 

 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 grad- 

 ual process of "anticipation," the pro- 

 thallus might become established before 

 pollination in any group of primitive seed- 

 bearing plants. There are other more 

 specialized rather than primitive features 

 in the complex structure of Lagenostoma 

 which might with much more reason be 

 invoked, to show that the seed of Lygino- 

 dendron does not form a step in the series 

 of forms leading to the Cyeadian ovule. 



But leaving this point out of considera- 

 tion, Chodat brings forward some strong 

 reasons for his conclusions that the Lygino- 

 dendreae were plants possessing 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 Lepto- 

 sporangiate ferns, and maerosporangia of 

 specialized type, containing a single macro- 

 spore. This group, therefore, Chodat re- 

 gards as a highly specialized group of 

 ferns, which, he considers, shows no par- 

 ticular connection with the Cycads, and 

 which may have formed the end in a series 

 of highly differentiated members of the 

 FilicincEe. 



Of the Medullosffi, on the other hand, 

 Chodat takes a very different view. Both 

 in the structure of their primary and sec- 

 ondary growth, as well as in their polys- 

 tely, 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-cham- 

 ber. Chodat considers the agreement of 

 the MedullosEe with the Cycadacese to be so 



