12 CIRCULAR 6 5 6, U. S. DEPARTMENT OF AGRICULTURE 



By July and later, wounds in all the treated plots showed no callus 

 formation and consequently they enlarged because of dying and 

 drying. 



Observation of pruning wounds where a branch is removed, in con- 

 trast with internodal or side wounds, indicates that the longitudinal 

 extension of pruning wounds when the tree is weakened is likely to be 

 greater than that of side wounds. The difference between spring and 

 winter treatments, therefore, would probably have been greater if the 

 data had been taken for pruning wounds instead of for side wounds. 

 When pruning or wounding is done just prior to excessive cold, en- 

 largement of the wound because of winter injury may result. The 

 work of Crenshaw and Cooley (6) showed that when subjected to 

 experimental chilling fresh wounds enlarged considerably as the result 

 of injury, whereas callused wounds and unwounded limbs showed no 

 evidences of injury. Winter pruning or wounding, therefore, involves 

 a hazard of winter injury about the wound, which does not exist in 

 spring pruning or wounding. The winters were mild during the ex- 

 perimental wounding reported in this circular; so enlarging of 

 wounds by cold injury was probably not so pronounced as it would 

 have been in a year having extremely low temperatures. 



The data reported by months in figures 1 and 2, respectively, were 

 combined into four seasonal groups, which are presented diagrammati- 

 cally in figures 4 and 5 to facilitate comparison of the shapes of wounds 

 made at different seasons of the year. 



Reaction of Wounds to Different Treatments 



The wounds with different treatments showed some fluctuations in 

 injury and healing. Such variation probably would have been much 

 less pronounced if more wounds had been used and if the trees had 

 been young and vigorous. The graphs show, however, that some 

 dressings caused less injury and gave better callus growth than others. 

 In order to facilitate comparison of one dressing with another, averages 

 of the enlarging or dying and of the closing or healing measured at the 

 ends of the first and the second season are reported in figure 6, A and 

 B. Such averages partially obscure certain aspects of the data that 

 the monthly records bring out, but they facilitate ready comparisons 

 of the relative effects of the different dressings. 



untreated wounds 



At the end of the first season, the average longitudinal extension 

 of the check wounds was less than that of those treated with No. 541 

 plus gasoline, No. 540, No. 540 plus gasoline, or white lead and linseed 

 oil, but it was more than that of those treated with No. 541 or shellac. 

 In average transverse diameter, which is an index of the amount of 

 callus formed, only wounds treated with shellac had healed better 

 than the untreated wounds (check). At the end of the second season 

 the average data for wound size showed the same general trend as 

 at the end of the first season. Some of the treatments showed still 

 more striking differences when the averages for the spring months, as 

 shown in figure 3, A and B, rather than those for the 12 months, were 





