428 THE WOAD AND WELD CROPS. 



Woad is a hardy plant, and although subject, no doubt, 

 to the same diseases and insect injuries as the turnip, 

 rarely suffers from them to the same extent. Owing to 

 the class of soils in which the crop is grown, the " mildew/' 

 which sometimes visits it in the autumn, is not followed 

 by such severe consequences. The "fly" (which is the 

 same that attacks the turnips) is the only enemy to be 

 dreaded, and the whole of the late sowings are sometimes 

 swept off by this insect pest. It is therefore always desir- 

 able to get the seed in as early as the season will allow, 

 for the double purpose of getting the young plants well 

 up before the " fly" makes its appearance in the fields, and 

 of being able to re-sow the crop before the season is too 

 far advanced, if the plant be destroyed by it. 



We know little or nothing of the chemistry of woad. 

 Before the chemistry of agriculture was thought worthy 

 of occupying the attention of scientific men, and, indeed, 

 before the processes of chemistry, especially of organic 

 chemistry, were sufficiently advanced and definite to 

 give their results any reliable value, woad was a rapidly 

 declining cultivation, and its foreign substitute indigo 

 was taken into the laboratory and investigated in its 

 stead. 



It is said to be an exhausting crop ; and this we may 

 more freely admit than in regard to the other crops against 

 which the same charge is made, as were we to begin with 

 a rich soil, to which no manure is given, arid from which 

 nearly the entire produce is sold, or at all events removed 

 off the land, the soil in which it is grown must as a 

 consequence be poorer at the end of the crop in fertilizing 

 ingredients than it was at the beginning, notwithstanding 

 the benefits received by the careful tillage cultivation 

 bestowed on it, especially in the eradication of the weeds 

 that spring up so plentifully when old grass lands have 

 been broken up. 



