ROOT -GALLS 91 



and die about the edges or in large irregular dis- 

 colored spots, but without the distinct pustular 

 marks of the parasitic fungi. There is a general 

 tendency for the foliage upon plants affected with 

 such diseases to shrivel and to hang upon the stem 

 for a time. One of the best illustrations of this 

 type of disease is the pear-blight. 



Still another class of diseases is characterized by 

 galls upon the roots. The galls upon greenhouse 

 plants, and upon outdoor plants in the southern 

 states, are usually caused by a true worm or 

 nematode, and the only complete remedy for these 

 is to freeze the soil. In glass houses there need 

 be no injury from these galls if the gardener is 

 careful to use no soil except that which has been 

 thoroughly frozen. Nematode galls are not known 

 to occur permanently in the northern states where 

 the ground freezes deep. There is another type of 

 root- gall, however, illustrated in Fig. 91, which 

 is coming to be common throughout the northern 

 states, and the cause of which is unknown. It is 

 probable that this disease propagates itself in the 

 stock, even if the galls are all removed before the 

 plant is set, although this point is not yet 

 thoroughly determined. It is supposed by many 

 careful observers, also, that land in which root- 

 galls have been produced is unsafe for the setting 

 of plants which are subject to the injury. The 

 best advice which can now be given in regard to 

 this difficulty is to set no plants which have galls 



