630 RA DIC A CEOUS ESCULENTS. 



towards forwarding the crop ; but, " why it does so, appears to be im- 

 perfectly understood, even by those who practise it. It is well known 

 that tubers are not solely formed on the underground part of the stem; 

 they are also formed upon the stem above ground in many varieties, 

 and these formations are of course green. Though formed at the 

 same time as those below, or later, yet they sprout directly, in the 

 same manner, even in the case of late varieties, the underground tubers 

 of which do not vegetate till the following spring. When, however, an 

 underground tuber is exposed to light, it becomes green, and thereby 

 is assimilated to the nature of the tuber produced above ground, and 

 like it disposed to sprout earlier than those not subjected to the 

 influence of light. It is not, however, necessary to green the sets for 

 a general crop, for if planted in time they come up early enough to 

 be safe from spring frosts without previous exposure, for the pur- 

 pose of greening ; but in the case of early plantations, with protection 

 if necessary, greening may be of some advantage ; and in the method 

 of retarding the sets so as only to plant them in July for a late young 

 crop, it is unavoidable, for the tubers would either grow too much or 

 rot, if they were not spread out in a dry cool situation, and conse- 

 quently one unfavourable for growth. Greening the tubers when taken 

 up is of great importance in forwarding and strengthening the early 

 crops. 



Taking up and Preserving a Crop, They should be carefully taken 

 up without injury ; not exposed to the sun or air, and at once stored 

 away in frost-proof cellars or pits, in layers or ridges of moderate 

 thickness, to prevent fermentation. If possible take them up in dry 

 weather, and store at once. If in pits, four feet wide and three feet high 

 will be quite enough. A turf, with the earthy side next the pota- 

 toes, might be laid on to keep the soil from mixing with them. Then 

 one foot of earth should follow, and this in severe weather might be 

 thatched over with litter to exclude frost. Buried in this way, potatoes 

 will keep well without sprouting or losing their flavour. 



Diseases, Insects, fyc. The potato is subject to the curl in the 

 leaves, which, when it has once taken place, cannot be remedied, but 

 which may, in general, be prevented by using healthy sets from the 

 middle or top end of the tuber, and by good culture in well pulverized 

 soil, dry at bottom. The heating and fermenting of sets, after they 

 have been cut, often produces the curl and other diseases ; and some 

 particular soils and manures seem to be the cause of the scab in the 

 tuber. These diseases, however, are more common in fields than in 

 gardens. A change of variety, or of sets of the same variety from 

 a different locality, is frequently resorted to, more especially in field 

 culture, as a general preventive of disease in the potato. None of 

 these methods, however, have checked the ravages of what is now 

 so well known as the potato disease. This has hitherto baffled 

 the power of the hybridizer and the cultivator. It created the Irish 

 famine, and still threatens to destroy the potato crop. Though less 

 virulent than it was, it has been occasionally very destructive in 

 many districts. It attacks the potato in the last stages of growth 



