378 SCIENCE PROGRESS 



BOTANY. By E. J. Salisbury, D.Sc, F.L.S., University College. 

 London. 



Cryptogams.'. — In a concluding paper {Trans. Roy. Soc, Edin- 

 burgh, No. 32), on the " Old Red Sandstone Plants from the 

 Rhynie Chert," Kidston and Lang give restorations of Rhynia 

 Gwynne-Vaughani, R. major, Hornea lignieri, and Asteroxylon 

 mackieiy and discuss their bearing on general problems connected 

 with the Pteridophyta. Asteroxylon, the most complex, it is 

 pointed out, presented an organisation comparable with that 

 of Psilophyton and encountered amongst present-day plants in 

 the Psilotacece, where too there is a relatively simple type of 

 construction associated with an absence of roots. A certain 

 measure of resemblance is also recognised to the Zygopterideas 

 amongst the ferns. The other three species show still further 

 simplification in the absence of leaves. A subterranean 

 rhizomatous region which bore absorbent hairs here gave rise 

 to a leafless and dichotomously branched cylindrical axis whose 

 finer branches bore terminal sporangia ; the simplicity here 

 exhibited renders comparison with the sporophyte of the 

 Bryophyta easier than in the case of other Pteridophyta, and 

 attention is called to the possibility that Sporogonites may have 

 been the fructification of a Pteridophyte. The suggestion also 

 made that these plants bring the Pteridophyta nearer to the 

 Algae seems to be a mere restatement that they are the most 

 simply organised Pteridophyta known, and appears to pre- 

 suppose a relationship which may in fact not exist. 



In connection with the foregoing it is interesting to note that 

 Holloway, in a further study of the prothallus and sporophyte 

 of Tmesipteris, emphasises the resemblance to the Rhyniacece. 

 Not only, as already shown, is the embryo of this plant much 

 simpler than that of other Pteridophytes in the fact that there 

 is no differentiation apart from shoot and foot, but the sporo- 

 phyte in its early stages of development closely resembles the 

 prothallus. It is at first a cylindrical structure exhibiting 

 dichotomous branching and entirely destitute of leaves. Thus 

 the ontogeny of Tmesipteris includes a phase comparable with the 

 adult condition of the Rhyniacese, which may perhaps represent 

 a phylogenetic recapitulation. There is, however, the possi- 

 bility that in both groups the extreme simplicity of construction 

 is an outcome of a common saprophytic mode of nutrition. 



Morphology and Anatomy. — Discussing in detail the leaf of 

 the Iridaceae {Ann. Bot., July), Mrs. Arber points out that both 

 in the ontogeny of the bud and the seedling there is nothing 

 to support the view advocated by Celakovsky and Velenovsky 

 that the bifacial leaf of Iris has arisen by concrescence. It is 

 shown that the leaves of various Iridaceae show considerable 

 resemblance in anatomical structure to the phyllodes oi Acacia. 



