xxxvi.] POTATO DISEASE, II. PASSIVE STATE. 327 



to decide whether repeated earthing -up, skilful haulm- 

 bending, and disinfecting with a hot-water apparatus and 

 assistants watching a thermometer, can be made a com- 

 mercial success. 



Disinfection, even if effectual, merely secures a possible 

 healthy start of the young potato plant, it by no means 

 secures the potato from the attacks of spores in June or 

 July ; these spores may come from neighbours' fields, 

 where the potatoes have not been disinfected, or from 

 tomatoes or other plants, and so all the labour of disin- 

 fection may be lost. It is obvious that, unless all the 

 seed-potatoes in Britain are disinfected, little or no good 

 can accrue from the use of a few sets of apparatus. Mr. 

 Jensen thinks this part of the subject " cannot be con- 

 sidered an unworthy object for legislation" (Gardeners' 

 Chronicle, p. 616, 10th May 1884), which we suppose 

 means that farmers should be compelled by law to use a 

 hot- water disinfecting apparatus before planting potatoes. 



Mr. Jensen appears to believe, judging from Mr Plow- 

 right's communications, that the planting of diseased sets 

 causes an early appearance of the disease, and that disin- 

 fection has a tendency to make the disease late. He 

 seems to conclude from this that constant disinfection 

 would at last make the fungus so late in its appearance 

 that the potatoes would be mature before the fungus could 

 grow. We are inclined to think, however, that the fungus 

 would change its nature so as to agree with the new habit 

 of the potato. Parasites always modify their habits to 

 suit any change of nature in their host. 



We have shown that Mr. Jensen's views were more or 

 less anticipated by Dr. Jeffrey Lang more than a quarter 

 of a century ago, and the earthing-up system has been 

 advocated both here and in America. We are inclined 

 to think that practical agriculturists would never have 

 dropped this treatment if it had contained the elements 

 of commercial success. 



Mr. Jensen's views will be found reported at length, 



