60 N. J. Agricultural Experiment Stations Bulletin 356 



June buds placed in healthy nursery seedlings grew well the first 

 summer and failed to develop any certain symptoms of disease, bui 

 there was some rolling of leaves late in the season. These trees grad- 

 ually decreased in vigor and appeared more sickly during the next 

 two years when they were removed. 



Observations indicate that it requires several months for symptoms 

 of yellows to develop following inoculation. The shortest period in 

 Xew Jersey experiments was from August of one year to May of 

 the next. The disease may be present in a tree for at least 4 seasons 

 before advanced symptoms appear. 



Breeding Experiments 



Pollen from a Dewey tree affected with yellows was used in cross- 

 ing healthy trees in 1916. A total of 45 trees were secured and planted 

 in orchard form in 1 ( H8. At the present time (1921) the trees are 

 all healthy. It seems safe to conclude that the pollen of diseased 

 •ices does licit transmit yellows. 



Factors Which Determine Size and Time of Maturitj of Fruit on 



Normal Trees 



A tree must he able to maintain a certain amount of growth and 

 vigor in order to produce fruit normally. A favorable temperature, 

 ample moisture and plant-food are essential to this end. Given favor- 

 able conditions for growth, tree development depends upon the taking 

 up ot crude plant-food by the roots, photosynthesis by the leaves and 

 translocation of the elaborated foods. 



When a tret- is young the elaborated food is used entirely for 

 growth, hut when fruit bearing begins ii is used for both vegetative 

 and fruiting processes. 



Rapidly growing peach trees quite frequenth set a few fruits a<- 

 early as the beginning of the second or third season, hut these fa" 

 oft in June because the elaborated food is used for growth. 



When peach trees are defoliated jusl before the fruit ripens it ma\ 

 •each good size hut is insipid and lacks flavor. In other words, the 

 starch and sugar forming processes of the tree have been greatly 

 reduced or removed. 



The rate of growth of a peach tree may begin to affect the size 

 of the fruits early in the season. Peaches on very rapidly growing 

 trees are commonly smaller than those on vigorous trees that are 

 checked in any manner that acts as a slight girdling. 



