368 GENERAL PLANT PATHOLOGY 



growth of the mesophyll cells and the space originally occupied by the 

 former is finally filled with the cells of the mesophyll. Excess of water 

 is one of the contributing causes in the formation of intumescences, 

 as also treatment of plants with poisons, especially copper salts. 



Abnormal succulence, as an hypertrophy, is such where plants with 

 normally thin leaves, develop thick ones in their place. Salt solutions, 

 if used experimentally upon certain plants, may induce succulency. 

 LeSage produced artificial succulence in the leaves of Lepidium sativum 

 by abundant doses of common salt, NaCl. The mesophyll cells were 

 elongated greatly. 



Fig. 145. — Cross-section through the wounded border of a cabbage leaf. The 

 hypertrophied mesophyll cells are enlarged into vesicular swellings. {Kilster, Palh- 

 ologische PJlanzenanatomie, 1903: 94.) 



Callous hypertrophy arises after an injury when the living cells of an 

 organ enlarge without division, especially at the edge of the wound, 

 where they may enlarge to many times their normal volume (Fig. 145). 

 As it frequently happens that cell divisions follow an injury, it is not 

 always easy to distinguish between callous hypertrophies and callous 

 hyperplasias. We find callus hypertrophies among the thallophytes, 

 as in Padina pavonia, and in the higher plants where the bark, wood 

 parenchyma, leaves are affected. Kiister produced callous hyper- 

 trophies near the upper surface of the cut by keeping one end of the 



