CULINARY ROOTS AND TUBERS. 123 



The Potato {Solamim tuberosum, fig. 179), in our social system, is 

 really a field crop, from the vast areas cultivated and from the large 

 quantity consumed. Nevertheless we give it a moderate place in the 

 garden. We grow only two crops, and for b ' 

 have used a variety known under the name 



Rivers' Ash-leaf Kidney. Early in Janu ^* 1 



we place a number of tubers in a shallow ] ^C^y ^^x ' 



in the vinery, on earth, and let them sprout 



Fig. 179. — Royal Ash-leaf Potato, 



slowly ; they are then planted in a layer of i =''^'=- 



nine inches of garden mould, placed over about two feet of leaves and 

 rotten dung to give a gentle and long-continued heat. These are fit 

 for the table about the middle of May, and last till the end of June, 

 a period at which a well-ripened new potato is a desideratum. For 

 our second crop the tubers are started in the same manner, and placed 

 out in rows two feet apart, and these come into use when the frame 

 crop is finished. The earth is drawn up to the haulm when the plant 

 is about six inches high, and that is all the cultivation which is re- 

 quired. The varieties of seedlings are now endless. By sowing the 

 seed of a good kind another good kind out of a certain number may 

 be fairly expected, and in selecting our kind we should be guided, 

 firstly, by its having a small haulm, as it then occupies little room ; 

 secondly, by the solidity of the tuber ; thirdly, by the weight of the 

 tuber; fourthly, by its flavour, and the absence of a sweet taste 

 fifthly, by its tuber being floury when cooked ; sixthly, by the smooth- 

 ne.ss of its surface, and shallowness of the eyes, so that when peeled 

 there is but little waste ; and seventhly, by its productiveness. 



Of late years the potato has been subject to disease, when 

 the haulm dies, the cells of the tuber lose their starch, and the cel- 

 lular tissue breaks down (fig. 180). From my observations I believe 

 the Aphis vastator, an aphis which has numerous .synonyms, attacks 

 the leaves ; the plant is then attacked with a parasite fungus called 

 the Penispora infesians, after which the plant dies and the tuber rots. 

 Some good botanists consider that the fungus, and not the aphis, is the 

 cause of the malady, and others believe that neither aphis nor fungus 



