PLASMODIOPHORA. 527 



mentary condition and twisted course of the vessels, and an 

 accumulation of transitory starch in the tissues. 



[The methods at our disposal for combating this parasite all 

 work indirectly. Its spores seem to retain their vitality for two, 

 three, or more years, hence one very evident measure is not to 

 plant the same crop in succession on land which has been attacked. 

 As, however, all Cruciferae are liable to injury from this source. 



Fig. 317. — Plasmodiophora brassicae on Turnip. (After Woronin.) 



neither would it be advisable to let say, turnips follow 

 cabbage or kohl rabi on infected land. For the same reason 

 weeds belonging to the order Cruciferae should not be allowed 

 to obtain a footing near land where plants liable to " finger and 

 toe " are under cultivation. In Scotland, where turnips are 

 necessary in all crop-rotations, a four-year rotation does not 

 give complete exemption from this disease, nor is five years 



