322 ON THE MATURATION OF GRAIN 



ent varieties of the potatoe plant have been dif- 

 ferently affected by the maladies, we cannot 

 conclude atmospheric miasma to be the prime 

 cause of these maladies. The state of the air 

 may, notwithstanding, partly account for the 

 higher grounds suffering less from the diseases 

 than the low grounds; because there transpiration 

 and aeration could be more fully carried on, and 

 the generative sap in consequence become more 

 carbonised, and thence better fitted for with- 

 standing the disease, and discharging vigorously 

 the vital and healthy functions of the plants. 



The diseases are not congenital. I have grown 

 sound tubers from infected ones. At present I 

 have six plants growing, the offspring of six 

 infected tubers, kept throughout the last winter 

 in a window, to prevent them from complete 

 infection, which are without speck of blight or 

 indication of murrain, though more than one half 

 of the tubers when planted were wholly disor- 

 ganized. Vigour of growth too is a great check to 

 the spread of the diseases. I had, last summer, 

 sixteen plants left in the soil during the winter, 

 on the same plot of ground with the spring 

 planted potatoes^ which had only a very few 

 leaves blighted, and but four potatoes diseased, 



