466 Pflanzenkrankheiten, 



übrig, die Pflanzen durch Schaffung ihnen zusagender Entwicklungs- 

 bedingungen möglichst zu kräftigen, da ganz gesunde kräftige 

 Pflanzen selten schwer von Blattläusen zu leiden haben. 



H. Detmann. 



Pethybridge, G. H., Investigations on Potato Diseases. 

 (Fourth Report). (Journ. Dep. Agr. and Tech. Instr. for Ireland. 

 XIII. 3. 1913.) 



The diseases dealt with in the fourth annual report are Phy 

 tophthora infestans, Sclerotinia sclerotiorum, Bacillus melanogenes, 

 Spongospora subterranea, Phytophtora erythroseptica, "Leaf Curl" 

 and "Leaf Roll" {Verticilliuni albo-atriim), and "Sprain". 



The experiments with P. infestans are chiefly concerned with 

 the relative advantages of spra3nng at different times and with 

 varying strenghts of Bordeaux or Burgund)?- mixtures. Cultural 

 experiments with the fungus made in the laboratory indicate that 

 the resistance of certain varieties of potato to the blight is due 

 to some peculiarity of internal structure. 



In the case of the other diseases, results previously obtained 

 are corroborated. Spongospora is transmitted by contiminated land, 

 and the best soil disinfectant was found to be flowers of sulphur. 

 Sulphate of potash also gave beneficial results. Experiments with 

 different varieties of potato indicate considerable Variation in sus- 

 ceptibility. 



Phytophthora erythroseptica is contracted from the soil, but 

 does not appear to be communicable in the pit. Mangels, Swedes, 

 and White turnips are attacked when artificially infected. 



A form of "Leaf-roU" is proved to be caused by the fungus 

 Verticillium albo-atriini, and is transmitted by mycelium in the 

 tubers, though all tubers from an affected plant may not contain 

 mycelium. E. M. Wakefield (Kew). 



Saxton, W. T., The Leaf- Spots of Richardia albo-maculata, 

 Hook. (Trans. Roy. Soc. S. Afriea. III. 1. p. 135—138. 1913.) 



In the white regions of the leaves of R. albo-maculata, the pali- 

 sade parenchyma has completelj'- disappeared, and only the spongy 

 mesophyll lies between the upper and lower epidermis. Very few 

 plastids occur in the cells. Growth takes place in the plane of the 

 lamina. It is suggested that certain cells of the mesophyll become 

 actively meristematic, a condition which is not extended to the 

 palisade, but is duplicated in both upper and lower epidermis. This 

 would cause a Splitting apart of the palisade in the centre of such 

 a group of meristematic cells, resulting in the structure described. 



E. M. Wakefield (Kew). 



Spinks, G. T., Factors affecting Susceptibility to Disease 

 in Plauts, Part I. (Journ, Agr. Sei. V. 3. p. 231—247. 1913.) 



The author has carried out a series of experiments with a view 

 to testing the effect of the nutrition of a plant on its susceptibility 

 to disease. Two varieties of wheat, "Little Joss" and "Michigan 

 Bronze", were tested with regard to Erysiphe graminis and Puccinia 

 glumarunt. Susceptibility to mildew and rust in wheat, and to mildew 

 in barley, was found to be increased by providing the plants with 

 large quantities of available nitrogen. Mineral manures decrease the 



