46 



SCIENCE 



[N. S. Vol. L. No. 1280 



as habitat-forms of one species, the differences 

 in structure being attributed to the influence 

 of water. In this as in many other recently 

 published papers it is satisfactory to find that 

 authors are now paying more attention than 

 formerly to the significance of structural fea- 

 tures as indices of climate and habitat. Mr. 

 Sahni's critical morphological study of the 

 branching of the leaf-trace in certain Car- 

 boniferous genera of ferns^* throws light on 

 some previously misunderstood anatomical 

 features and illustrates the value of the ap- 

 plication of broad philosophical generalizations 

 based on intensive study of allied forms. Miss 

 Holden's account of the anatomy of two 

 Paleozoic Cardaitalean stems from India ;'^^ 

 placed in the genus Dadoxylon, supply wel- 

 come information on the structure of plants 

 belonging to the Olossopieris flora: the occur- 

 rence of well marked rings of growth in the 

 wood of both species is a fact of special in- 

 terest from the point of view of the climatic 

 conditions under which the plants of the 

 southern flora flourished. A report of a Brit- 

 ish Association Committee published in 1917 

 summarizes opinions on the vexed question of 

 the classification^" of the older rocks of Gond- 

 wana land in which plants of the Glossopteris 

 flora are preserved. 



Eesearehes of both scientific and economic 

 interest into the composition and mode of 

 origin of coal have in recent years attracted 

 the attention of several workers. The most 

 important piece of work of this kind is that by 

 Dr. Stopes and Dr. Wheeler,^^ a happy combi- 

 nation of expert botanical and chemical knowl- 

 edge. The authors begin by defining ordinary 

 coal as a " compact, stratified mass of mum- 

 mified plants free from all save a very low 

 percentage of other matter," that is practically 

 a deposit of plants alone. It is rightly 

 claimed that too little attention has hitherto 

 been paid to research following logical de- 

 ductions from our knowledge of the chemical 



lilbid., Vol. XXXII., p. 369, 1918. 

 M Annals of Botany, Vol. XXXI., p. 315, 1917. 

 10 British Assoc. Eeport, 1917, p. 106. 

 17 Monograph on the Constitution of Ckjal. Dpt. 

 Scientific and Industrial Research, London, 1918. 



composition of plants. The authors deal with 

 modes of accumulation of coal-forming vege- 

 table material action of the solvents on coal, 

 the effect of heat, distillation at different tem- 

 peratures, microscopic evidence bearing on the 

 constitution of coal derived both from the 

 coal itself and from the petrified tissues pre- 

 served in the calcareous nodules of certain 

 coal seams. A very useful bibliography is ap- 

 pended. Mr. Lomax^^ has continued his micro- 

 scopical analysis of coal seams and discusses 

 the part played by different plants and parts 

 of plants in the composition of coal. Similarly 

 Mr. Hickling,'-' who writes on the micrope- 

 trology of coal, reviews previous work and 

 gives the results of original observations; he 

 attributes differences in coal rather to the re- 

 sult of varying degrees or varying modes of 

 alteration than to differences in the nature of 

 the original constituents. 



3. Mesozoic Plants. — Dr. Arber's memoir, 

 published shortly before his death, on the 

 older Mesozoic floras of New Zealand,-" is a 

 particularly welcome contribution to our 

 knowledge of the little known botanical his- 

 tory of that country. He deals with Triassic- 

 Ehsetic, Jurassic and Cretaceous plants. Tha 

 author shows that no Palaeozoic flora has so 

 far been discovered: the absence of any un- 

 doubted examples of the common southern 

 hemisphere genus Glossopteris leads him to 

 express the view that New Zealand did not 

 form part of that extensive continent known 

 as Gondwana land in the Permo-Carbonifer- 

 ous x>eriod. An account is given of a remark- 

 able petrified forest at Waikawa, Southland, 

 consisting chiefly of some conifers and well- 

 preserved osmundaceous stems. Dr. Arber's 

 work clears up many obscure points and cor- 

 rects erroneous statements by previous au- 

 thors. 



Important contributions have been made to 

 our knowledge of Jurassic plants, notably the 

 description of a new genus, Williamsoniella, 



18 Trans. Instit. Mining Engineers, Vol. L., Pt. 

 I., p. 127, 1915. 



19 Ibid., Vol. LIIL, Pt. III., p. 137, 1917. 



20 New Zealand Geol. Survey, Paleontological 

 BuUetin No. 6, Wellington, 1917. 



