BY R. GREIG SMITH. 



245 



In checking the formation of gum on valuable plants, such as 

 fruit trees, the healthiness of the tree should first be considered 

 and means taken to ensure the efficient drainage of the soil and 

 the absence of decaying vegetable matter such as buried stumps. 

 The proper manuring of the tree will next suggest itself so that 

 the plant might be stimulated to a healthier condition. The 

 excision of the part or parts from which the gum is oozing will 

 probably be of little avail, because it is probable that the bacteria 

 are producing the gum in the tissues between the wound and the 

 growing point of the stem or branch. If the gum should exude 

 from a branch only, then the pruning of that branch would 

 probably be beneficial. 



Any chemical remedy for the prevention of gum-formation 

 must consist in the application of a salt injurious to the bacteria. 

 The effect of a nitrogenous salt would be indirect. Other salts 

 might act directly, and with regard to these something might be 

 learned from laboratory experiments. We have seen that a trace 

 of a succinate or citrate is beneficial, and that some salts were 

 indifferent, while others were injurious. But in the former tests 

 an optimum medium was not employed, and it, therefore, appeared 

 to be wise to repeat the experiment by adding salts to the optimum 

 medium and noting the depression which they exerted upon the 

 yield of slime. Accordingly tubes of the optimum medium were 

 prepared and salts added to the extent of 0-5%. 



The effect of Salts upon the Optimum Medium at 17° C. 



Salt added. 



No salt 



Potassium chloride 

 Sodium ,, 



Calcium ,, 



Magnesium sulphate 

 Sodium phosphate . 

 Magnesium sulphate 

 Calcium chloride 

 Potassium nitrate 

 ,, sulphate 



Grms. of slime from 100 c.c. of 

 medium.* 



26 

 19 

 15 

 16 

 16 

 17 



17 



12 

 20 



Levulose 2, asparagine O'l, potassium citrate O'l, tannin 01, agar 2'0 water 



