DISEASES OF PLANTS 



73 



were reached by Finch and Kinnison (1933). Among other 

 aspects of the problem they examined soils on which rosette 

 appeared, but could find no relation between any soil factor and 

 the incidence of rosette. The effects of a number of substances 

 on affected trees were examined. These substances included 

 salts of iron, magnesium, manganese and zinc. Three treatments 

 were employed: (1) placing the dry material in holes bored 

 in the trunk of the tree, (2) spraying leaves with solutions 

 of the substances or dipping the leaves in the solutions, and 

 (3) injecting the solutions into the tree trunks. With zinc salts 

 a great improvement in the condition of the trees was effected 

 by all three methods of treatment. In some cases, but by no 

 means in all, some improvement was observed with the use of 

 iron salts, a result which could be attributed to the presence of 

 zinc as an impurity in the iron salts, especially as no improve- 

 ment resulted with the use of purer iron salts. No benefit 

 occurred as the result of treatment with either magnesium or 

 manganese salts. 



Determinations of the zinc content in different parts of 

 the terminal 6 in. of some shoots taken from the top of pecan 

 trees were made; the results are summarized in Table V. They 

 show that the shoots of the tree affected with rosette contained 

 very much less zinc than those of healthy trees, while in a rosetted 

 tree treated with zinc chloride by solid injection and in which 

 recovery from rosetting had taken place there was already after 

 8 weeks a very considerable increase in zinc content. 



Table V. Zinc content of leaflets, petioles and stems of pecan 

 (Carya olivaeformis) . The quantities are given as p. p.m. of 

 dry matter. (Data from Finch and Kinnison) 



Condition of tree 



Healthy 



Healthy 



Rosetted 



Rosetted ; then treated with 6 g. 



zinc chloride injected in trunk 



(55 days after treatment) 



Finch and Kinnison also published data of the zinc content 

 of irrigation waters used in different districts of Arizona for 

 supplying pecan plantations. Five out of six of these waters 



