Decembee 25, 1908] 



SCIENCE 



905 



In the absence of such organic selective 

 structures at the outset, it may be worth 

 while to look for inorganic agencies that 

 may perhaps have performed in a crude 

 way the functions which the organic struc- 

 tures came later to perform in a much 

 superior way. It is not clear that a 

 selective coneentrative agency can be found 

 in the large water-bodies, independent of 

 life, for their tendency is diffusive and 

 equalizing rather than coneentrative. Can 

 it be found in the soil? 



To form a definite picture of the conditions 

 which may have been presented by certain 

 soils, let a foreland lying between extensive 

 uplands and a permanent water-body of 

 appropriate salinity be chosen as a concrete 

 example. In such a situation a constant 

 water-level shovild have prevailed not only 

 at moderate but at graded depths beneath 

 the surface. The underground water 

 should have received accessions percolating 

 basinwards from the uplands bearing what- 

 ever soluble materials the uplands could 

 furnish, while, on the other side, there 

 should have been waters percolating land- 

 ward from the water-body bearing such 

 salinity as it possessed, while more or less 

 spray from the water-body was scattered 

 by landward winds over the surface and 

 fed the soil from above. The measure of 

 water-movement in the one direction or the 

 other must obviously have depended on the 

 balance between the precipitation and the 

 evaporation on the adjacent land which 

 varied with seasons and localities. The 

 underground waters thus supplied by the 

 slightly fluctuating water-table should have 

 been carried up by the capillary passages 

 of the soil to horizons of evaporation and 

 concentration at or near the surface. The 

 graded depth of soil above the water-table 

 should have furnished unlimited adapta- 

 tions to the porosity of the soil-mantle and 

 to the meteorologic conditions of the sea- 

 sons and the special situations. 



The horizons of concentration by capil- 

 larity and by evaporation were affected by 

 all degrees of insolation from direct sun- 

 light, at the immediate surface, to all meas- 

 ures of shadowing below, furnished by the 

 soil itself. The substances deposited within 

 the soil and the substances leached from it, 

 alike modified its porosity in their own 

 special ways, and such deposits as were 

 formed in the soils should have developed 

 porosities of their own. Isolated cells and 

 tubes may thus have been formed by traver- 

 tine and similar deposits in the pores of the 

 soil. As already implied, the capillary 

 feeding from the water-table, when the bal- 

 ance set that way, and the partial evapora- 

 tion of the solutions within the pores of the 

 soil near or at the surface, must have pro- 

 duced concentrations of the non-volatile 

 substances carried by the capillary waters 

 into these upper horizons. Between these 

 upper concentrated solutions and those be- 

 low there should naturally have followed 

 inter-diffusion and osmotic action, and thus 

 there should have sprung up in the soil a 

 circulation somewhat analogous to that of 

 the plant ; indeed, it may not be going too 

 far to suggest that this circulation within 

 the soil is more than a simple analogue of 

 the systematic circulation which is defi- 

 nitely organized in the plant structure: it 

 may possibly be its genetic forerunner. 

 The larger cavities within the soil were in- 

 evitably connected by constricted passages 

 which were liable to be partially or wholly 

 filled with porotis precipitates or with in- 

 organic colloids, and these chains of pores 

 might thus come to serve a circulatory func- 

 tion which was an actual precursor to that 

 circulation from cell to cell through mem- 

 branous walls which distinguishes com- 

 pound plants. It is even more probable 

 that the circulation within an earth-pore, 

 partially isolated from adjacent earth-pores 

 containing solutions of different density, 

 might develop a circulation closely like that 



