278 M. H. Hoffmann on Fermentation. 



the vegetation of certain Fungi exerts upon organic liquids, we 

 are no longer surprised," says M. Hoffmann, u at the devasta- 

 tions which it causes among plants. We can no longer dispute 

 upon the question whether the Fungi are the cause, or a con- 

 comitant of these maladies, and we must admit that, under 

 certain combinations of temperature, atmospheric condition, &c. 

 these effects are due naturally to these Fungi and Infusoria, and 

 see in them redoubtable enemies of plants and animals, and 

 perhaps also of man." 



With regard to the potato- disease, M. Hoffmann refers to the 

 valuable discoveries of M. Speerschn eider, but gives a succinct 

 account of the results of his own experiments, from which he 

 draws the following conclusion : — After continued heavy rain, 

 accompanied by a low temperature and want of sun, Perono- 

 spora Solani is developed in prodigious quantity on the leaves of 

 the potato plant, and kills them, as if they had been burnt. 

 The mature spores fail to the ground, and, when the moisture 

 and heat are sufficient, germinate and send down their filaments 

 into the tubers, of which the bark is still tender ; the filaments 

 reach the interior of the tubers, introduce themselves into the 

 cells, of which they decompose the walls and amylaceous grains, 

 and thus cause the destruction of the tuber. 



This furnishes the indication of a rational treatment for the 

 cure or prevention of the potato-disease. As soon as, under the 

 atmospheric combinations above described, the foliage of the 

 potato-plants appears to be attacked by a whitish blight (Perono- 

 spora), and appears as if burnt, there is danger of rotting of the 

 tubers — at least unless dry weather supervene. The best method 

 is to cut off the stalks, and it would be well to water the ground 

 above the tubers with milk of lime or a solution of chloride of 

 lime, or to sulphur it, as has been done with the grapes, with 

 the object of destroying the spores of the fungus. 



If the disease has begun to affect the potatoes, it would be 

 necessary, before heaping them up, to wash and dry them. The 

 removal of the herbage appears to be of no consequence when 

 the tubers are developed. According to M. Hoffmann's obser- 

 vations, the period of this development, in the part of Germany 

 where he dwells, is seven weeks after the first planting of the 

 tubers, fourteen weeks after planting for late potatoes, and 

 twelve weeks after planting for spring potatoes. Under any 

 circumstances, the removal of the leafy parts towards the end of 

 August cannot be prejudicial. 



