DISCOVERY 



153 



t wide range. At the same time it is difficult to tind 

 in tliis means an adequate explanation of the fact that 

 practically half the Antarctic lichens and 30 per 

 cent, of the mosses are found also in the Arctic. A 

 simpler and more credible explanation may be 

 found in the idea that the species in question are 

 either cosmopolitan and have not been discovered 

 in low latitudes, or that they are species which have 

 been crowded out by stress of competition in low- 

 latitudes where conditions more favourable to plant 

 growth mean more contest for location. 



There seems to be much evidence that the present 

 Antarctic flora, like the sub-antarctic flora, is mainly 

 of Fuegian origin, and has migrated eastward before 

 the prevailing westerly winds, both bird and wind 

 transport having played their parts. Ice transport 

 plays no part outside the pages of a few textbooks. 

 This evidence I have analysed elsewhere, and there is 

 no reason, in the light of later knowledge, to modify the 

 conclusions. It might, however, be noted that former 

 land connections which there is every reason to believe 

 connected Antarctica at least with South America, if 

 not New Zealand and Australia, cannot be held 

 responsible for any of the present Antarctic flora. 

 Apart from the fact that these land connections 

 probably were lost in Tertiary times, there is ample 

 evidence that a great extension of glaciation occurred 

 at a later date. This must effectively have destroyed 

 every vestige of vegetation in Antarctic regions. The 

 present flora must have migrated to the Antarctic in 

 recent geological times, since the period of maximum 

 glaciation. 



The literature of Antarctic botany is considerable. For a 

 discussion of the origin of the flora reference may be made 

 to " Problems of Antarctic Plant Life," R, N. Rudmose Brown, 

 in Report on Scien. Results S.Y. Scotia, vol. iii, 1912, and 

 papers in same volume hy J. Cardot on Mosses, F. E. Fritsch 

 on Fresh-water A)g;e, and O. V. Darbishire on Lichens. Con- 

 tributions of importance occur in Wissen. Erg. der Schwedischen 

 Siidpolar Exp., vol. iv, including J. Cardot on Moss flora, 

 O. V. Darbishire on Lichens, and C. Skottsberg on Algae ; and 

 in British Antarctic Exp., 1907-9, Report on Scien. Invest., 

 W. and G. West on Fresh-water Algae. 



nitrogen. It is now well established that there are 

 bacteria present which have the amazing property of 

 " fixing " the nitrogen of the air, and handing it over 

 to plants in a form of which they can make use ; and 

 not one process, but a whole chain of processes, is 

 involved in their many-sided activities. It is not easy 

 to see how life could ever have been developed to 

 its present scale apart from them. 



A less friendly bacterium from the agriculturist's 

 point of view is that which competes with crops for 

 the nitrates present in the soil. The decomposition 

 of the cellulose which forms the framework of plants 

 has engaged the attention of McBeth and Scales in 

 America and of Hutchinson and Clayton at Rotham- 

 sted, and important knowledge has been acquired as to 

 the action of carbohydrate substances such as sugar 

 and straw, which are present as the residues of former 

 crops, and which serve the bacteria as a source of 

 energy sufficient to enable them to use the nitrates 

 for their own purposes and to deprive the crops of 

 them. 



Carbohydrates, however, are not the only nitrogen- 

 free organic compounds that occur in the soil. Other 

 compounds, though present in smaller quantities, 

 may be of considerable importance. Phenol, which 

 we know better under the name of carbolic acid, and 

 related compounds are found in the soil, being 

 formed by bacterial action in the intestines of animals 

 and probably even in the soil itself. The amount of 

 phenol produced, though small, is by no means negli- 

 gible ; thus Mooser calculated that with a dressing of 

 liquid manure anything from 30-74 lb. of phenol 

 may be added to the acre. Such compounds, if they 

 persisted in the soil, would accumulate, and ultimately 

 prove a source of plant poisoning. Dr. Brenchley 

 at Rothamsted has, indeed, shown that in water- 

 culture experiments the addition of small doses of 

 phenol is poisonous to plant growth. The disappear- 

 ance of phenolic compounds even from heavih^ manured 

 soU indicates that a mechanism must exist by which 

 they are removed or destroyed. 



The Bacteria of the Soil 



And the Utilisation of Organic 

 Antiseptics 



By p. H. H. Gray, M.A. 



liolliamsted Eipcrimenlal Slalicn 



The great importance to plant-life of the presence of 

 bacteria in the soil was first recognised in connection 

 with their powers of dealing with that vital element. 



The Disappearance of Antiseptics 



The problem of the destruction of phenol compounds 

 in soil became of practical importance owing to the 

 use of such substances in the tomato-growing industry 

 as soU-sterilising agents. In glass-houses, cresylic 

 acid, which is a substance of this kind, is applied to the 

 soil for the purpose of killing such destructive tomato 

 pests as the eel-worm, Heterodera. It is fomad, how- 

 ever, that unless added in strong concentrations, 

 phenol and cresol disappear from the soil with consider- 

 able rapidity, so that their full effect on the pests is 

 not felt. .\ parallel case is that of naphthalene, which 



