168 SIXTEENTH BIENN IAL REPORT 



The first question we must ask ourselves then is, what constitutes a vigorous 

 tree in a condition right for maximum production? Investigations carried on in 

 recent years, cliiefly at tlie Experiment i^tation of the Oregon Agricultural Col- 

 lege, lead US to believe that the reason for maximum production lies deep down 

 in the food supply of the tree. In other words, we have found in our investiga- 

 tions that wood growth and satisfactory bearing come only when there is a proper 

 balauce between the nitrogen and carbohydrates in the tree. (By carbohydrates 

 we mean such Compounds as sugar, starch, cellulose, etc., manufactured by leaves 

 of plants by using CO2, and through the agency of sunlight working upon the 

 Chlorophyll of the leaves.) 



Dr. E. J. Kraus, formerly of the Oregon Agricultural College, and Dr. Kraybill 

 worked upon this problem of the nitrogen-carbohydrate ratio; *the results of 

 their work being published in Station Bulletin No. 149 of the Oregon Agricultural 

 College Experiment Station. Dr. E. M. Harvey, who has succeeded Dr. Kraus in 

 the field of research, and Mr. A. E. Murneek, his assistant, are continuing along 

 this same line of investigation, amplifying it more and more to meet the Problems 

 of the fruitgrower. 



To sum up briefly the meaning of the nitrogen-carbohydrate theory, and to 

 Show the influence of the proper balance between the nitrogen and carbohydrates, 

 the following four conditions of growth may be noted : 



1. N+C. Nitrogen plentiful plus carbohydrates very limited. Result, no 

 growth to the tree and no fruit. This condition is not found except in pot experi- 

 ments where factors can be absolutely controlled. 



2. N+C. Nitrogen abundant plus carbohydrates abundant. Exuberant 

 growth, bringing the tree into bearing late; little fruit. This is a condition 

 usually found upon young trees before they come into bearing. 



3. N+C. Nitrogen slightly limited plus abundant carbohydrates results in a 

 fair growth to the tree and in heavy bearing. This condition is found in prac- 

 tically all of our best cared-for orchards that are showing vigor and regulär 

 bearing. 



4. N+C. Nitrogen limited plus carbohydrates abundant is shown by small 

 gi'owth of wood, weak fruit Imds and little fruit. It is an easy matter for 

 orchards that have been in bearing for some time to gradually change from con- 

 dition three to condition four. 



How may the orchardist discover vv'hether his trees are in the proper condition 

 of balance or not? In a recent bulletinf by Roberts of Wisconsin, we find that 

 he establishes a cori-elation between regulär annual bearing and the length of 

 fruit spur growth. He divides fruit spurs into four classes based upon length 

 and Performance. These classess, of course, blend more or less into each other. 



1. An unfruitful fruit spur — about one-eighth of an inch annual growth on 

 the average. 



2. Spurs that blossom but do not set fruit — average annual growth three- 

 sixteenths of an inch. 



3. Spurs setting fruit — average annual growth one-half inch. 



4. Long spurs producing only leaf buds — average annual growth three-fourths 

 of an inch and over. 



It should be understood at this point that Roberts was working on the Wealthy 

 apple chiefly, and other apples may differ somewhat from this in actual measure- 

 ments, though the principles are exactly the same. Roberts found that the long 

 spurs are so well supplied with nitrogen and grow so fast that the leaves are 

 spread over such a wide distance as to make it impossible for them to supply the 

 spur with sufficient carbohydrates for fruit production. On the spurs in elass 

 three, while the spur is considerably shorter, more leaves are concentrated near 

 the point where the fruit is to be formed, and consequently more carbohydrates 



♦Vegetation and Reproduction with Special Reference to the Tomate. 

 tWisconsin Bulletin No. 317 : Off-year Apple Bearing. 



