DISEASES OF PLANTS. 857 



DISEASES OF PLANTS. 



The effect of aqueous solutions upon the germination of fungus 

 spores, F. L. Stevens {Hot. Gaz., 26 (1898), No. 2, pp. 377-406, Jig. 1).— 

 The primary object of the investigations here reported was to ascertain 

 with some degree of accuracy the strength of various solutions which 

 are necessary to prevent fungus growths. The bearing of this ques- 

 tion upon the relation of a fungicide to its efticieucy is apparent, and 

 it seems important to study the principles underlying their action. By 

 means of the van Tieghem hanging drop, cultures were made of Botrytis 

 vulgaris, Macrosporium sp. from the fruit of Datura tatula, Glaospo- 

 rium musarum, Uromyces caryophyllinus, and Penicillium crustaceum. 

 The methods of the experiments are fully described and the different 

 chemicals used are enumerated. The solutions used were made by 

 adding the molecular weight of the salt or acid taken in grams to 1 

 liter of water. In all more than 1,500 cultures were made, from which 

 the author deduces the following conclusions: Mercuric chlorid is the 

 strongest chemical used in its toxic effect upon fungi, while potassium 

 cyanid is remarkably weak considering its great toxic action on animals. 

 Various fungi offer different resistance to poisons, and the limits of 

 resistance may vary in the same species. Alcohol and sodium chlorid 

 seem to have a stimulating effect. 



In general the results obtained accord with the theory of hydrolytic 

 dissociation. A chemical may be twice as powerful as auother against 

 one fungus, but may act upon another in an entirely different ratio. 

 The spores of fungi are much less su.-ceptible than the roots of seed- 

 lings. Bordeaux mixture, as ordinarily formed, contains far more 

 copper than would be necessary if dissociated into copper ions. The 

 cathions Hg, H, and Ou and the anions CN, CrG 4 , 0r 2 O 7 , and OH are 

 poisonous, while the halogen anions are not poisonous. 



Uromyces offers the greatest range in its susceptibility to poisons. 

 Secondary spores of anthracnoses increase in abundance under the 

 adverse conditions of a toxic solution. Spores protected by actual 

 contact with others may germinate and the tube grow in a solution 

 which would have prevented the germination of the spore had it been 

 in contact with it. Peculiar knotty or twisted kyplne frequently result 

 from the attempt to grow in a poisonous solution. A spore may be able 

 to germinate and grow slightly iu a solution in which it is unable 

 to attain its full development. Potassium permanganate at certain 

 strengths acts as a selective stain, differentiating the uredo from the 

 teleutospores of Uromyces caryophyllinus. 



Bread may be moistened with a solution which will prevent the ger- 

 mination of the spores, but after evaporation of the solution the spores 

 can then grow. An occasional spore may germinate and grow per- 

 fectly normally in a solution which prevents hundreds of normal spores 

 around it from germinating. Penicillium in a nutrient medium offers 



