ROOT CROPS. 75 



work of destruction in any young turnip, cabbage, or other 

 cruciferous crop near at hand. 



The following analyses (by the author) show the changes 

 which occur within turnip roots during the early stages 

 of the growth of Plasmodiopliora hrassicce : — 



Albuminoids in healthy roots 9-92 per cent. 



„ diseased „ {minus nodules). . 5-23 „ 

 „ nodules (with fungi) 18-61 „ 



The above analyses show that the growth of the fungus 

 lessens the percentages of albuminoids or nitrogenous 

 substances in the roots. As Plasmodiophora (like all 

 fungi) cannot " manufacture " albumin and requires it — it 

 extracts this life-giving substance from the living cells of 

 the host-plant. 



Prevention. — (1) Do not allow the cruciferous weeds, 

 more than is possible, to choke the hedge-sides of the fields 

 and ditches under cultivation. (2) As the spores of this 

 fungus retain their vitality for several years under favour- 

 able circumstances, when land has borne an infested crop, 

 the best thing to do is to remove decaying roots, stumps, 

 etc., and burn them. (3) Rotation of crops, i.e., allow two 

 or three years to elapse before again sowing cabbages, tur- 

 nips, or other root crops. (4) Whenever possible, avoid 

 working the land in a wet condition. (5) The selection 

 of good seed ^ and the most approved methods of culture 

 are means of preventing this disease. 



Cure. — After clearing the land, give it a good dressing 

 of gas-lime or lime and soot. 



This chapter surveys the life-histories of parasites 



' Turnip seeds have often been adulterated with charlock, •' Indian 

 rape," and other seeds of the Brassicaceee. 



