RECENT ADVANCES IN SCIENCE 133 



contributes useful notes on Prof. Lacroix's great memoir on 

 the Laterites of French Guinea (Noitv. Arch, du Mus., 1914). 

 Prof. Lacroix had the advantage of examining a large number 

 of fresh railway sections showing the complete passage from 

 the underlying unaltered rock, through the various stages of 

 laterisation, to the hard surface crust or cuirasse. With regard 

 to the origin of laterite he comes to the conclusion that it is 

 not due to the direct attack of the atmosphere or surface-water, 

 but that the process of laterisation is intense wherever the slope 

 of the ground is such as to permit the infiltration of water and 

 allow it to remain for a long time in contact with the rocks. 

 The reactions of which laterite is the outcome occur with 

 greater intensity in tropical countries because of special climatic 

 conditions, but go on, although not to the same degree, under 

 other climates. This, of course, accounts for the distribution 

 of laterite only within or near tropical regions. 



The closely related substance, bauxite, is dealt with by 

 W. J. Mead in a paper on "The Bauxite Deposits of Arkansas" 

 {Economic Geology, January 191 5). The bauxite has been de- 

 veloped by the surface weathering of a nepheline-syenite, and 

 occurs either in situ or as lenses intercalated with Tertiary 

 sediments, and deposited by Tertiary streams. The open texture 

 of the rock produced by the decomposition of nepheline is held 

 to be essential to the change of the kaolinised felspar of the 

 syenite into bauxite. It is also shown that alumina is somewhat 

 concentrated towards the base of the deposits by solution of 

 the bauxite and its subsequent redeposition at a lower level. 



BOTANY. By Prof. F. Cavers, D.Sc, Goldsmiths' College, London. 



In plant physiology, Prof. H. H. Dixon and his collaborators 

 have published further work on the various problems connected 

 with ascent of sap in trees (Sci. Proc. Roy. Dublin Soc. 15). By 

 determining (by the method of weighing the parts of cut-out 

 photomicrographs) the percentage of the total cross-section of 

 the wood occupied respectively by vessels, fibres, cells, walls, 

 etc., they claim to have disproved the view that protoplasmic 

 streaming in the living wood-cells may cause the transpiration 

 current. They find also that large amounts of sugars are present 

 in the transpiration stream, their concentration being greater 

 than that of the electrolytes present, and suggest that the distri- 

 bution of carbohydrates is a function of transpiration no less 



