234 Diseases of Greenhouse Crops 



older varieties, the following are reported as being 

 especially susceptible to stem rot: Crimson King, 

 Scott, Jubilee, La Purite, De Graws, Servan, Silver 

 Spray, Flora Hill, McGowan, Portias, Boston Mar- 

 ket, Craig, Lawson, Winson, and Lady Bountiful. 

 The newer varieties do not seem to possess any more 

 resistance than the older ones. For a description of 

 the causal organism and methods of control, see p. 20. 



Root Knot 



Caused by Heterodera radicicola (Greef ) Muller. 



Symptoms. Root knot is characterized by swell- 

 ings of the roots. Affected plants are decidedly 

 dwarfed, yellowish, and sickly looking. The roots 

 of diseased plants are extensively knotted, and 

 lumpy. For a description of the causal organism 

 and of methods of control, see p. 28. 



