PEACH DISEASES 305 



ing cells, and comes in contact with living protoplasts which are 

 stimulated to release an enzyme; this enzyme causes gelat- 

 inization of the primary lamella. This gelatinized gum con- 

 stitutes the exudate which is forced out through pits into the 

 ducts and adjacent wood cells and fibers. Some of the various 

 causal factors involved in gummosis of the peach follow: 

 (1) frost ; (2) fungi, such as Sclerotinia cinerea, Valsa leucostoma, 

 Coryneum Beijerinckii, and others; (3) bacteria, such as Bac- 

 terium Pruni; (4) insects. Among the other factors which have 

 been listed as possible causes of gummosis are: (1) lack of 

 balance between the nutritive processes ; (2) galls on the roots ; 

 (3) excessive rainfall ; (4) severe pruning, particularly when 

 the peach is pruned during the period of its greatest vegetative 

 activity, that is, from April to August ; (5) poor cultivation ; 

 (6) deep planting ; (7) adverse soil conditions ; (8) adverse 

 atmospheric conditions; (9) hail; (10) over-bearing. It 

 will be seen that gumming may be due to any one or several 

 of the following classes of factors : (1) climate ; (2) adverse 

 soil and nutrition; (3) animal or plant parasites; (4) un- 

 favorable cultural conditions. 



Control. 



The remedy involved will depend somewhat on the cause. 

 In any case the local affected areas should be cut out wherever 

 this procedure is feasible. In those cases where the exact 

 cause is determined, the measures of control may be found in 

 the discussions given under that heading for the individual 

 diseases concerned (Frost-cankers and gummosis, page 300 ; 

 gum-flow due to Sclerotinia cinerea, page 275 ; to Valsa leuco- 

 stoma var. cincta, page 302 ; to Coryneum Beijerinckii, page 313 ; 

 to Bacterium Pruni, page 310). In general the phenomenon 

 of gumming may be remedied by making conditions favor- 

 able to growth of the tree. It is always essential to learn the 

 nature of the exciting factor. (See also Cherry Bacterial-Gum- 

 mosis, page 181.) 

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