MICRO-NUTRIENT PROBLEMS 53 



introduction by various methods of liquids and solutions into 

 plant organs, whether under pressure or not, and their spread 

 therein'. 



In a long discussion on injection of plants as a physiological 

 method, Roach (1939) describes no less than ten ways in which 

 injection can be carried out ; each of these has its own particular 

 value. The ten injection methods are these: 



1. Intervenal leaf injection. 



2. Leaf- tip injection. 



3. Lestf immersion (Anderssen). 



4. Leaf-stalk injection. 



5. Shoot-tip injection. 



6. Branch-tip injection. 



7. Shoot injection (Leach) and branch injection (Collison, 



Harlan and Sweeney). 



8. Injection of individual branches. 



9. Injection of individual branches together with their 



roots. 

 10. Injection of whole trees. 



Not all these methods of introducing material into plants 

 have been designed for the purpose of diagnosing mineral 

 deficiencies, nor are all of them equally valuable for this purpose, 

 although any one of them could no doubt serve to demonstrate 

 the existence of such deficiency. But on the whole the methods 

 in which leaves or young shoots are injected are those which are 

 most useful for diagnostic purposes, while those in which larger 

 branches or a whole tree are used are more generally useful for 

 some other purpose, as, for example, the cure of a deficiency. 



The principle underlying injection methods of diagnosis is 

 that the introduction into a leaf of a salt of an element in which 

 the plant is deficient will produce a definite response which is in 

 the direction of a cure of the deficiency. The most usual response 

 is a colour change in the leaf which generally becomes greener ; 

 sometimes increased rate of growth of a leaf occurs. These 

 responses are best observed when leaf areas permeated by the 

 nutrient are in close juxtaposition to control non-permeated 

 areas; a difference in colour between permeated and control 



