764 



'club-root' disease 



fected with the disease, and on puUing up a diseased plant, a 



mere blunt, woody stump is often found to be all that remains 



underground. 



The roots of healthy plants in dry soils are frequently unable 



to keep pace with the loss of water by transpiration in bright, 

 _ hot weather, and 



the leaves conse- 

 quently become 

 limp; during the 

 night transpiration 

 is much reduced, 

 and the roots soon 

 make good the 

 loss of water, the 

 leaves in the morn- 

 ing exhibiting their 

 ordinary fresh ap- 

 pearance. In 

 ' clubbed ' plants, 

 however, the root- 

 system is more or 

 less permanently 

 injured, and the 

 leaves, after wither- 

 ing in the daytime, 

 do not regain their 



Fig. 258.— 'Clubbed' root of cabbage: a young dubbed normal turgld COn- 



adventitious root ;« older clubbed part ; c insect-galls, two cut ^if-i^n Hnrincr thp 



across to show hollow interior ; i decayed stump of old root ""-'O" uuililg uic 



(half natural size), _^^|.f. 



Some of the rounded thickenings or galls, about the size of a 

 pea or marble {c. Fig. 258), met with upon the lower parts of the 

 stems of cabbages and on the outside of turnip and swede ' roots,' 

 are caused by the larvse of a weevil {Ceutorhyncluis suldcollis), and 

 are in no way connected with ' club-root ' disease, although both 



