398 ANNUAL KECORD OF SCIENCE AND INDUSTRY. 



subject. The emission of perspiration or moisture from the 

 leaf is thus prevented, and the plant becomes surcharged 

 with moisture, which rapidly rots the stems and leaves, the 

 mycelium preying upon the tissues. 



It is very common to find a species of aphis upon the leaves 

 and stems of the infected plant, and many persons have as- 

 cribed to this minute insect the origin and perpetuation of 

 the evil. It is, however, the opinion of most authorities that 

 the disease is primarily caused by the fungus, which attacks 

 perfectly healthy plants, and that the aj^hides simply find in 

 the resulting decay a suitable and agreeable resting-place. 

 4 ^,Oc^o^>er, 1872,332. 



WHY THERE IS NO REMEDY FOR THE POTATO DISEASE. 



In reply to an assertion in the London Magazine that our 

 ignorance of a satisfactory remedy for the potato disease is 

 rather a stigma ujoon modern science, an eminent naturalist 

 retorts that the investigations necessary to determine the de- 

 sired remedy require large expenditures of time and money ; 

 and that, if those who are practically interested in the subject 

 our governments or the farmers do not think it sufficient- 

 ly worth their attention to induce them to employ scientific 

 men for the special object of working out this problem, the 

 omission to do so can not be imputed to the latter. Very 

 little, indeed, so fir as we know, can be done to arrest the 

 disease, from the fact that the infection spreads so rapidly 

 that the first intimation of its presence may be the destruc- 

 tion of the crop in an entire field. It is said that potatoes 

 escape Avith little or no disease in the neighborhood of chem- 

 ical works; which is due possibly to the efi*ect of the sul- 

 phurous acid or other gases that are noxious to the fungus 

 growth, without injuring the more highly organized potato 

 plant. 



The application of finely divided sulphur is beneficial here, 

 as in other plant diseases. It is stated that if, as soon as the 

 disease has attacked the fields, the stems be all cut down 

 close to the ground, the infection will not extend to the 

 tubers; and when the crop is nearly ripe this may be a ju- 

 dicious application, but it necessarily has the effect to stop 

 any further growth. Even in this case, however, the potatoes 

 may be serviceable for seed for the coming year. After re- 



