142 Pflanzenkrankheiten. — Bacteriologie. 



dass es mö.glich ist wie bei der Plasrnopara vüicola so auch bei der 

 Rebenperonospora das Auftreten der Peyonospora voraus zubestim- 

 men und dementsprechend rechtzeitig gegen die Krankheit vorbeu- 

 gend zu spritzen. 



Ueber das Franzosenkraut {Galinsoga parvißora) finden sich 

 weitere Mitteilungen. Es hat nur eine örtliche Bedeutung als äus- 

 serst lästiges Unkraut, da es nur auf sandig humosem Boden vorkommt. 



Ausser diesen wichtigeren Punkten finden sich noch sehr zahl- 

 reiche Angaben über tierische und pflanzliche Schädlinge, die aber 

 nur rein lokales Interesse besitzen. Drei sehr gute Abbildungen 

 (Wurzelknöpfe an Birnenwurzeln, Podosphaera lencotricha am Apfel- 

 baum und eine durch Aeichen Aphelenchus ormerodis zerstörte 

 Erdbeerkultur) verdienen hervorgehoben zu werden. 



Boas (Weihenstephan). 



Greaves, J. E., Some factors influencing ammonification 

 and nitrification in soils. (Cbl. Bakt. 2. XXXIX. p. 542-560. 

 1913.) 

 Some virgin soils contain As and may cultivated contain this ele- 

 ment in large quantities; sometimes in the water soluble form, 

 sometimes in the insoluble form. So called insoluble arsenical 

 insecticides are not totally insoluble after being applied to a soil, 

 even though the soil be high in calcium and iron. The greatest 

 quantity is soluble where Paris green has been applied and the 

 least where lead arsenate has been applied. Arsenic trisulfide appa- 

 rently becomes more soluble on Standing in soil. One hundred parts 

 per 100 000 of sodium arsenate may be applied to a soil rieh in Ca 

 and Fe without materially decreasing the ammonifying or nitrifying 

 powers of that soil, but smaller quantities may stimulate quite 

 markedly this activity. Zinc arsenite, lead arsenate and arsenic 

 trisulfide stimulate the ammonifying activities of a soil, and their 

 toxicity is not very marked until comparatively large quantities of 

 arsenic are present, and the two former reduce the ammonifying 

 and nitrifying activities only one half when 1120 parts per 1 000 000 

 of arsenic are present. Paris green exerts a marked toxicity on the 

 ammonifiers, even when present in small quantities and when 

 present in large quantities it practically stops ammonification in 

 soil. 'AU the Compounds tested stimulated nitrification, being least 

 where arsenic trisulfide was used and greatest where lead arsenate 

 was applied. Arsenic trisulfide and Paris green when present in 

 large quantities nearly stopped nitrification. Arsenic stimulated 

 ammonification and nitrification when present in soils in small 

 quantities, but when present in very large quantities it becomes 

 toxic. The stimulating activity of the various Compounds added to 

 the soil upon ammonifying organisms, and especially to the nitri- 

 fying organisms is partly due to the anion and partly to the cation. 

 And much of their action may be due to their influence upon in- 

 jurious species Water soluble arsenic may exist as such in soils 

 to the extent of 82 parts per 1 000 000 without entirely stopping 

 ammonification and nitrification and large quantities of ammonia 

 and nitric nitrogen may be produced in a soil containing 50 parts 

 per 1000 000 of water soluble arsenic. Measured in terms of their 

 influence upon ammonification and nitrification as it takes place in 

 the soil the toxicity of lead arseniate is followed by zinc arsenite 

 and arsenic trisulfide and greatest with Paris green. 



Matouschek (Wien). 



