32 EXPERIMENT STATION BULLETIN 351 



however, that the main features of the results are of sufficient interest to 

 warrant recording here. 



In 1930, results were published (Tech. Bui. 42) of a study concerned 

 with relation between the composition of new growth of non-bearing 

 spurs on the Baldwin tree and the formation of blossom buds by similar 

 spurs the following spring. A highly significant positive correlation was 

 found between the nitrogen content of the spurs and the formation of 

 blossom buds. This result was in such striking contrast to the generally 

 accepted ideas on this subject that it appeared desirable to repeat the ex- 

 periment. Samples for the first experiment were taken in 1925 and those 

 for the second in 1931. 



A prf^liminary report of the results of this second experiment was 

 presented in 1936 at the Rochester, New York, summer meetings of the 

 American Association for the Advancement of Science, but it was not 

 submitted for publication. 



For the spurs sampled in 1931 a highly significant positive correlation 

 was found between starch and the formation of blossom buds. The find- 

 ings for the two sets of samples were not in agreement; in fact, they were 

 exactly contradictory. 



That the two seasons were unlike is shown by the rainfall for May 

 and June, just previous to the usual time for the differentiation of blossom 

 buds and to the time the samples were taken. In 1925 the total rainfall 

 for these two months was 4.83 inches and in 1931 it was 8.55 inches. 

 Other environmental factors also may have been effective. 



At any rate it appears that in 1925 the general level of carbohydrate 

 accumulation in fruit spurs was adequate for blossom bud formation, and 

 that such formation was limited by the extent of accumulation of nitrogen 

 compounds. In 1931 this situation was reversed. 



T. G. Phillips, G. F. Potter 



The Nature, Causes, and Prevention of Winter Injury to Fruit Trees 



This study was continued to determine methods of more accurately 

 measuring winter injury as it occurs. A method was developed to meas- 

 ure accurately the internal tree temperature at any depth and at any in- 

 stant by means of the potentiometer-thermocouple. Copper-Constantan 

 Thermocouples, No. 30, were inserted in a peach tree as follows: 



A hard steel wire 1 m.m. in diameter was sharpened and then in- 

 serted into the bark and cambium layer and pushed downward along the 

 southwest side of the tree. Being flexible this wire easily moved through 

 the thin-walled cells of the cambium, a distance of 2.5 inches parallel to 

 the surface of the trunk. This distance is necessarv to avoid incorrect 

 readings due to thermal conduction. To insert thermocouples at a great- 

 er depth, holes of 2.5 m.m. in diameter were drilled downward from the 

 lower crotch of the tree, a distance of at least 2.5 inches. A greater dis- 

 tance would, of course, be necessary when working with trees of larger 

 diameter. 



A small plug of cotton was forced into the holes where the lead \\ ires 

 emerged from the tree, and the cotton plug was then covered with graft- 

 ing wax. Lead wires were run through a 1.5 inch pipe to a room 100 feet 

 distant in which our Leed and Northrup Portable Potentiometer Indicator 



