xvii.] CLUB-ROOT OF TURNIPS, CABBAGES, ETC. 97 



be due to insect punctures on the tap-root when the plant 

 is young. But excrescences caused by insect punctures 

 are quite distinct from true clubbing. Curtis, in his 

 Farm Insects, has rejected the idea of Aphides being the 

 cause of clubbing. 



To see the nature of the fungus of club-root, one of the 

 smaller spindle-shaped swellings must be cut in two, as 

 on the line A, B, Fig. 34, and from one of the exposed 



FIG. 34. CLUB-ROOT DISEASE OF TURNIPS, ETC. 



Root of young Turnip with Clubs. 



One-half natural size. 



surfaces a thin slice must be cut. If this is done in July, 

 and the slice is viewed as an opaque object and magni- 

 fied 10 diameters, it will be seen, as in Fig. 35, faintly and 

 curiously mottled and clouded. If an extremely thin 

 atom is now cut off and viewed as a transparent object 

 with a power of 200 diameters, it will be seen as at Fig. 

 36. The cause of the mottling will now be seen to be 

 due to the presence of a yellowish stringy slime or plasma, 

 H 



