322 DISEASES OF FIELD & GARDEN CROPS. [CH. 



high and sharp moulding, by which the upper surface of 

 the uppermost tubers is covered with about 5 inches of 

 earth. To effect this, it is necessary that the ridge be so 

 high that the top of it is 10 inches or 12 inches above 

 the surface of the adjoining furrow, whilst the ridge must 

 be very broad at the bottom : this system also requires 

 that the tops of the potatoes shall be moderately bent to 

 one side, with a view to prevent the rain-water from run- 

 ning down the stems and thus carrying the spores outside, 

 as Mr. Jensen thinks, to the tubers. By this contrivance 

 more spores will fall between than upon the ridges. Mr. 

 Jensen advises that the potatoes be not lifted before the 

 diseased foliage has quite withered, because the tubers 

 will become sprinkled with the fungus spores from the 

 leaves and stems. " For six days," Mr. Jensen writes, 

 " the harvested tubers will appear to be sound, but on 

 the seventh or eighth day, according to temperature, they 

 will suddenly show marks of the disease. It is not even 

 sufficient that the leaves are withered before the lifting ; 

 they must have been so for three or four weeks, otherwise 

 many spores will be found capable of germinating, and 

 thus be dangerous to the tubers when the latter are taken 

 out of the ground." Mr. Jensen sums up his views with 

 the following general rules : 



1. The ground must be thoroughly worked, so that the 



potatoes may be planted in friable earth, which 

 affords a better means of protection than a lumpy 

 soil. 



2. The potatoes should be planted (pretty early) at a 



distance between the rows of at least 28 in. or 30 

 in. A greater distance is not required by the 

 system, but if closer it would impede the protective 

 moulding. 



3. The first moulding must be flat, so that the formed 



ridge be broad on the top and only about 4 in. 

 high. This moulding may be repeated if it is 

 thought advisable. 



