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SCIENCE 



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



argument against their root nature, as the 

 same origin is ascribed to the roots of Phyl- 

 loglossum and to those produced on the 

 rhizophores of Selaginella. Probably, in- 

 deed, as Bower points out in his masterly- 

 exposition of the "Origin of a Land 

 Flora," in dealing with the Lyeopodiales, 

 "the root in its inception would, lilie the 

 stem of these plants, be exogenous." Ac- 

 cording to the "recapitulation theory," 

 indeed, the exogenous formation of the 

 roots in the embryo of certain Lycopods, 

 as well as of the first root of Isoetes and the 

 first root of the Filicales, might be regarded 

 as the retention of a more primitive char- 

 acter in these particular organs. The 

 roots of Stigmaria, even if exogenous, 

 might therefore merely represent a more 

 ancestral stage. This difference between 

 the roots of Isoetes and the rootlets of 

 Stigmaria may, however, be more apparent 

 than real, for my colleague. Dr. Lang, has 

 drawn my attention to the fact that there 

 appear to be in Stigmaria remnants of a 

 small-celled tissue on the outside of what 

 has generally been taken to be the super- 

 ficial layer of the Stigmarian axis, and a 

 careful investigation of this point inclines 

 me to agree with him that very probably 

 the Stigmarian rootlets were actually 

 formed like those of Isoetes, somewhat be- 

 low the surface layer, which, after the 

 emergence of the rootlets, became partially 

 disorganized. Should this surmise prove 

 correct when apices of Stigmaria showing 

 structure come to light, the last real differ- 

 ence between the rootlets of Isoetes and the 

 rootlets of Stigmaria will have disap- 

 peared, and the view for which Professor 

 Williamson so strongly contended will be 

 finally established. 



While a careful comparison of Isoetes 

 with the extinct Lycopodiaceous plants 

 may be taken to finally settle its systematic 

 position, the Psilotacese have been some- 



what disturbed by such comparisons. 

 Placed formerly without much hesitation 

 in the phylum Lyeopodiales, certain fea- 

 tures in their organization, such as the 

 dichotomy of their sporophylls, and the 

 structure of their fructification generally 

 have suggested affinity with that interest- 

 ing group of extinct plants, the Spheno- 

 phyllales. Their actual inclusion in this 

 group by Thomas and by Bower may seem, 

 perhaps, somewhat hazardous, considering 

 the differences existing between the Psilo- 

 taceffi and Sphenophyllum ; and the more 

 cautious attitude of Seward, in setting up 

 a separate group for these forms, seems on 

 the whole more satisfactory than forcing 

 these aberrant relatives of the Lycopods 

 into the somewhat Procrustean bed of 

 Sphenophyllales, which necessitates the 

 minimizing of such important differences 

 as the diehotomous branching of the axis 

 and the alternate arrangement of their 

 leaves, though the latter character allows, 

 it is true, of some bridging over. But, 

 even adopting this more cautious attitude, 

 the study of the Sphenophyllales has been 

 of great help in coming to a clearer under- 

 standing of certain morphological pecul- 

 iarities of the Psilotacea3, quite apart from 

 the flood of light which this synthetic 

 group of Sphenophyllales has thrown upon 

 the relationship of the Lyeopodiales to the 

 Bquisetales. 



More far-reaching in its bearing on the 

 relationships of existing plants has been 

 the study of those interesting fern-like 

 plants which seem to show in their vege- 

 tative organs a structure possessing both 

 fern-like and Cyeadian affinities. Full of 

 interest as these so-called Cycadofilices 

 were in their vegetative organization, they 

 were destined to rivet on themselves the 

 attention of all botanists by the discovery 

 of their fructifications. No chapter in the 

 recent history of paleobotany is more thrill- 



