RECENT ADVANCES IN SCIENCE 47 



independent of the kind of nutrient salt, its original concen- 

 tration or the volume employed. 



In relation to the more beneficial effect of liming on Barley 

 than on Rye, Hartwell and Pember have tested the two species 

 in water, and sand cultures to which sulphuric acid had been 

 added (Soil Science). For both types of culture the depression 

 of growth was almost the same for the two species. Soil extract, 

 however, from an acid soil had a much more deleterious effect 

 ^n the Barley than on the Rye, and the same effect was pro- 

 duced when the ash of the soil extract was brought into solu- 

 tion. It was found that the different effect of acidity on the 

 two species was due to aluminium. The latter appears to 

 have a more pronounced toxicity for Barley than Rye, and it 

 is suggested that the advantages of phosphating and liming 

 soils may be due to precipitation of active aluminium. 



The ecology of lichens is the subject of a paper by R. Paul- 

 son, dealing especially with Epping Forest (Essex Naturalist, 

 191 8). Of the sixteen species recorded from the trunks of the 

 hornbeam, eight are members of the Graphidiaceae. The terri- 

 colous lichens are similar to those of Oak woods but less 

 numerous and luxuriant. In the woods north of London the 

 Graphidiaceae are very poorly represented and mostly found 

 in Quercus sessiliflora woods on young trees 1 5-2 5 years 

 old. The lichen flora of Beech woods is not abundant, except 

 in well-lighted spots on the North Downs, but Lecidia crustu- 

 lata and Rhizocarpon confervoides occur, particularly on the 

 pebbles in the Beech areas of Epping. Lists of lichens from 

 five Calluna heaths comprise twelve species of which half are 

 Cladonias, two belong to the genus Bceomyces, two to Lecidia 

 and one species to each of the genera Cetraria and Peztigera. 



Pathology. — The specialisation of fungal parasites belong- 

 ing to the genus Septoria has been the subject of investigation 

 by W. S. Beach (Amer. Journ. Bot. Jan. 191 9). As the result 

 of numerous inoculation experiments, he has demonstrated 

 that some species are probably differentiated into biologic 

 forms. Most of the species are limited in their power of in- 

 fection to one or few closely related hosts. Thus Septoria 

 brunellce is probably restricted to Prunella vulgaris, but S. 

 lactricola from Lactuca canadensis not only infected other 

 species, but also Sonchus oleraceus though not S. asper. The 

 age of maximum susceptibility varies with the host. In the 



