DISEASES AND INSECT INJURIES. 361 



its entire extent, carried each year a crop of rape for 

 seed. Since that period, however, our home consump- 

 tion has enormously increased, 1 while our home pro- 

 duction has in like proportion decreased; and it would 

 therefore appear to be a subject worth our farmers' atten- 

 tion whether we could not, under an improved system 

 of cropping, and with the vast mechanical advantages we 

 now possess, profitably increase our production of rape seed, 

 and thus, so far, lessen our annual money contributions to 

 the agriculture of foreign countries. 



The diseases and insect ravages incidental to the crop 

 "are well-nigh identical with those already described as 

 affecting the turnip crop. The " mildew" is less frequent, 

 owing probably to the growth of the plant shading the 

 soil, and preventing evaporation from its surface. The 

 "fly" is equally as destructive in its attacks on the earlier 

 sown plants, which, however, owing to the difference in 

 their form of development, escape the injuries inflicted by 

 the " gall- weevil " (Ceutorhynchws pleurostigma) on the 

 roots of the turnips (see p. 324), and also those peculiar 

 forms of disease known as "fingers-and-toes" and "anbury." 



The caterpillars of the "turnip saw-fly" are. however, 

 equally disposed to take up their quarters on the leaves of 

 the rape, and to commit the same ravages as they do with 

 the turnip crop ; while one of the butterflies which visits 

 our fields has been named Pontia napi the "rape-seed 

 or green- veined white butterfly" from its predilection for 

 this plant, whose caterpillars, hatched on the leaves, com- 

 mence their work of destruction as soon as they appear. 

 Fortunately their numbers are kept down by an ichneu- 



1 The quantity of rape seed imported for the three years ending 1858 was 

 763,332 qrs., or an average of 234,444 qrs. per year; while the quantity of oil- 

 cake imported during that same period was 263,150 tons, or 87,716 tons per 

 annum, of which a considerable proportion probably one-third was rape 

 seed. The consumption of rape oil, which is also largely imported, is enormous. 

 In 1850 the North Western Railway alone required an annual supply of no 

 less than 40,000 gallons, equal to the produce of about 200 acres of crop. 



