CHAPTER XXIII. 

 EXCRESCENCES. 



Herbaceous excrescences, or galls Erineum Intumes 

 cences Corky warts, etc. Pustules Frost-blisters 

 Galls and Cecidia Root nodules. 



Excrescences, or out-growths of more or less 

 abnormal character from the general surface of 

 diseased organs, are very confimon symptoms, and 

 widely recognised. They are due to hypertrophy 

 of the tissues while the cells are young and 

 capable of growth, and may be induced by a 

 variety of causes, among which the stimulus of 

 insect-punctures and of the presence of insect 

 eggs are best known ; but that of fungi, though 

 less widely recognised, plays an equally important 

 part, and, as we shall see, galls and other ex- 

 crescences may be due to widely different agents. 

 Galls or Cecidia are protuberances of the most 

 varied shapes, colours, and sizes found on her- 

 baceous parts attacked by insects, fungi, etc. In 

 the simplest cases the insects only pierce and 



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