Recent Studies on Peach Yellows and Little Peach 43 



most nitrogen contained the least. The behavior of the trees agrees 



perfectly with the principles of plant growth previously stated. 



Development of Advanced Symptoms of Yellows Inversely Proportional 

 to Rate and Vigor of Growth 



It has been noted that yellows appears to develop most rapidly in 

 bearing trees and especially in neglected trees. We have noted 

 further that yellows is similar in its behavior to the effects of slow 

 growth, to girdling and to interference with downward translocation 

 of foods. We can now understand why the prominent symptoms of 

 yellows develop more rapidly in bearing, slow growing or checked 

 trees. If the condition of the trees is such that the translocation of 

 carbohydrates is slow, the influence of yellows will cause prematuring 

 and other symptoms within a shorter time than would be the case 

 in normal rapidly growing trees. Or in other words, if a tree is 

 growing rapidly, it will require a longer period for the disease to 

 check the growth sufficiently to produce the advanced symptoms of 

 yellows than it will if the growth is already checked by fruiting, by 

 injury or by neglect. 



Starch Tests with Diseased Nursery Trees 



Fxaminations were made late at night and in the early morning of 

 the leaves of some of the peach trees propagated in the nursery from 

 diseased buds to note whether the interference with the transfer of 

 carbohydrates was as great as in bearing trees. The morning exam- 

 ination showed that there was less starch in the leaves of diseased 

 nursery trees than is usually the case in diseased bearing trees. 

 Nursery trees grow rapidly and this behavior is in keeping with the 

 observations on diseased bearing trees, that with more rapid growth, 

 less starch is found in the midribs of the leaves in the early morning 

 of each day. 



Storage of Starch in Branches and Roots 



After it had been determined that differences in growth could be 

 readily correlated with the amount of starch found in the leaves in the 

 early morning, further tests were planned to determine the relative 

 amounts of starch in the branches and roots. 



Starch tests of the twigs, branches and roots of peach trees at 

 Vineland (1913 and 1914) showed that the amount of starch in the 

 branches and roots steadily increased until the falling of the leaves; 

 and at that time the slow growing but vigorous trees, or those on the 

 plots receiving no nitrogen, contained a much larger percentage of 

 starch than the roots and branches of the more rapidly growing 



