266 



The Plant World. 



Bouget, in a paper on the geographical botany of the 

 Pyrenees, points out the interesting fact that plants which at 

 lower levels grow only on siliceous soils are found on limestone 

 in the upper alpine zone. The limestone soil absorbs and holds 

 heat better than siliceous soil, and this, according to the writer 

 named, is the probable cause of the observed change of habitat. 



A Danish writer who has given special attention to the dis- 

 ease of crucifers caused by Plasmodiophora Brassicae, finds that 

 its geographical distribution in Denmark is determined more 

 by conditions of soil than by means of dissemination. West of 

 a certain boundary formed by a glacial moraine the soil is sandy 

 and the disease is common, while east of the same boundary the 

 soil is more fertile and is free from the Plasmodiophora. Chalk 

 in the soil and soil moisture are both important factors, and it 

 is recommended to supply chalk and drain the land on which 

 cabbage, turnips, etc., are grown 



Potter, in recent experiments on checking parasitic diseases 

 of plants, found that a concentrated solution obtained from 

 orange juice charged with the waste products of metabolism 

 of Penicillium italicum was capable of preventing the extension 

 of decay in oranges attacked by this fungus. These, and other 

 results reported by him, indicate that the waste products of 

 metabolism of parasitic organisms may be successfully em- 

 ployed in checking the progress of plant diseases due to the ac- 

 tion of these organisms. 



Lind, who has studied the distribution of the gooseberry 

 mildew, Sphaerotheca mors uvae, since its appearance in Sweden, 

 rinds that man is the worst conductor of infection, and next are 



