Diseases of the Plum 333 



conspicuous on the tree trunks ; but may be found on 

 the small twigs and fruit spurs, and even on the fruit. 



Many fruit growers have the notion that this gum- 

 ming is caused by some insect. Some attribute it di- 

 rectly to the borer. Others suspect fungi or bacteria 

 of being the cause of the trouble. According to the 

 best information now at hand, all these suppositions 

 are partly right and partly wrong. 



It seems that the cell walls in the several tissues 

 of the stone fruits are peculiarly apt to break down or 

 disintegrate. Just what may be the chemical nature 

 of this change need not now concern us. But at any 

 rate the substance of these cell walls becomes semi- 

 fluid and exudes as the white gum first noticed by the 

 orchardist. This soon absorbs water, swells, and finally 

 becomes discolored after exposure to the air, rains, etc. 



This disintegration of the cell walls is incited by 

 any sort of mechanical or physiological injury to the 

 tissues. Splitting of the branches from wind, or over- 

 bearing, abrasions from single-tree or hames, bruises 

 from hailstones, the excavations of borers, freezing of 

 the trees; are common mechanical causes. The com- 

 monest fungous origin of gummosis is in the attacks of 

 the fruit rot or monilia. This disease seems to injure 

 the tissues in such a way as to be especially favorable 

 to the formation of gum. Improper methods of cul- 

 tivation have also been assigned, with some show of 

 reason, as a cause in certain cases. Some writers on 

 the subject charge the trouble in more general terms 

 to weakened vitality. This phrase does not mean 

 much; and it is doubtful if it has much basis in fact, 

 aside from the various more nearly ultimate causes 

 mentioned above. Beach concludes* that "the exces- 



*S. A. Beach, Gumming of Stone Fruits, American Gardening, 19:606. 

 August 27, 1898. This is the most important recent contribution to the 

 subject in America. 



