562 abstracts: phytopathology 



BOTANY. — Generic types with special reference to the grasses of the 

 United States. A. S. Hitchcock. Amer. Joiirn. Bot. 5: 248-253. 

 1918. 

 Stability in nomenclature has been aided by the adoption of the 

 idea of types, a genus being based upon a type species and a species 

 upon a type specimen. In the present paper the author summarizes 

 a study that he has made in applying the principle of types to 255 

 genei'ic names of grasses. In 8 genera the type species has been desig- 

 nated. Of those in which no type was designated at the time of publi- 

 cation, 150 were based upon single species. In the remaining cases 

 types have been selected on the principle that the type must be one of 

 the species included in the genus as originally published and should 

 be the species or one of the species that the author had chiefly in 

 mind at that time. The difficulties are greatest in the Linnaean genera. 

 Several examples are given illustrating the methods used in the selection 

 of the type species. A. S. H. 



PHYTOPATHOLOGY.— T'Ae groivth of the potato-scab organism at 

 various hydrogen-ion concentrations as related to the comparative 

 freedom of acid soils from the potato scab. L. J. Gillespie. Phy- 

 topathology 8 : 257-269. 1918. 

 A study was made of the viability of a number of strains of the 

 common potato-scab organism m culture media adjusted to various 

 hydrogen-ion exponents. Two synthetic media and a medium pre- 

 pared fr im potato extract were used, and especial attention was paid 

 to the buffer action of the culture media. In media at the initial ex- 

 ponent 5.2 the growth was slower and generally less vigorous than at 

 less acid exponents. Under some conditions individual strains were 

 somewhat more sensitive to acidity, but the differences did not lead to 

 any consistent distinctions among the strains. Sometimes the organ- 

 isms succeeded in growing well in a medium which had initially an ex- 

 ponent of 5.2 or even 4.8, but the growth was accompanied by a marked 

 decrease of acidity, and the manner of growth gave reason to doubt 

 whether even in these cases more than a pooi growth can occur at such 

 exponents 



It would appear that the acidity of the Caribou loam, which is 

 known to be generally immune from the common (corky) potato scab, 

 is often of sufficient intensity to exert in the soil an injurious action 

 on the causal organism. The acidity of the Washburn loam, on the 



