118 



VEGETABLE FORCING 



tomato in Fig. 38, of lettuce in Fig. 39. Serious derangement 

 of the normal life functions is caused by the worms, which 

 results in the development of irregular galls and the im- 

 perfect nutrition of the plant. Evidence of infested roots 

 may be indicated by the leaves becoming sickly or 

 yellowish or by the stunted and dwarfed appearance of 

 the entire plant. If the attack is serious, yields will be 



, , greatly diminished or the 



plants may die before any 

 crop is harvested. The fleshy 

 enlargements are watery and 

 tender, and they provide 

 ready entrance for fungi and 

 bacteria, which may cause 

 rapid decay and additional in- 

 terference with the nutrition 

 of the host plant. 



Nematodes migrate very 

 slowly, not more than a few 

 feet a year, but they may be 

 introduced or distributed in 

 the greenhouse by means of 

 infested soil, manure and 

 plants. They may be con- 

 veyed about the establishment 

 on the shoes of the workmen 

 and on the various tools 



Fig. 39. Galls on lettuce roots which are Used for tillage Op- 

 caused by nematodes. 



erations. 



Numerous preventive measures have been advocated. 

 Chemicals of various kinds have not proved practical. 

 Lime is probably of no value, for the worms will live for 

 several days in a saturated solution of lime. Formalin 

 has been used with slight success. Freezing, desiccation 

 and inundation are valuable to some extent, but they are 

 not regarded favorably by greenhouse growers. The 



