146 HORTICULTURE, FORESTRY, FLORICULTURE 



which are brought to bear upon the tree prior to and during the 

 period at which fruit-bud formation takes place. In the practice of 

 such orchard operations as are designed to influence or control fruit- 

 bud formation, it appears that such operations should be more effect- 

 ive in the spring and early summer than at other stages of develop- 

 ment. (U. S. E. S. B. 178; Va. E. S. R. 1910.) 



Leaves of Fruit Plants. An abundance of healthy leaves is 

 essential to the rapid growth of the tree and the regular development 

 of fruit. The leaves combine and elaborate the crude sap from the 

 soil and the carbon dioxid of the air into new compounds suitable 

 for wood growth and fruit. Spraying, even in years of unfruitful- 

 ness, is often of advantage because it permits the maturing of a full 

 crop of healthy leaves. 



Fruit. A true fruit, strictly speaking, is the ripened seed vessel 

 and its contents. This agrees with the horticulturist's definition of 

 such fruits as apples, pears, peaches, apricots, plums, gooseberries, 

 and currants, but in the case of strawberries, blackberries, and mul- 

 berries it would permit only the single grains on the sides of the 

 berries to be called fruits, whereas the fleshy center is the part referred 

 to by the fruit grower when he speaks of them as fruits. (U. S. E. 

 S. B. 178.) 



Flower. The time of flowering in the spring of a given variety 

 of fruit, is dependent upon a number of causes or conditions, chief 

 among them being, first, the number of positive temperature units 

 received in the spring preparatory to flowering ; second, the stage of 

 development of the flower-buds as dependent upon the climatic con- 

 ditions of the summer and fall preceding the flowering; third, the 

 fruiting of the trees, whether light or heavy the year previous to 

 flowering; fourth, soil conditions and the amount of plant food pres- 

 ent in the soil; and fifth, the individual characteristics and state of 

 health of the tree or plant. 



From the data presented it would appear that there is but little 

 relationship between the time of flowering and the temperature in 

 the spring, up to the time of flowering, while there appears to be 

 considerable evidence that the temperature and other climatic con- 

 ditions during summer and fall preceding flowering has much to do 

 with the time of flowering. 



As a general statement, it is true that a given variety of fruit 

 trees will flower when it has received a reasonable number of tempera- 

 ture units, but it is also true that this number is not constant, but 

 rather variable, and on this account cannot be used in formulating 

 a physiological constant. 



On the other hand, there are greater reasons for constructing 

 a physiological constant from the sum of positive temperature units 

 received during the summer, fall, and spring preceding the life event, 

 though, as has been stated, other factors enter into the calculation. 

 But, eliminating these factors, it seems reasonable from the evidence 

 presented, a physiological constant can be formulated from the cli- 

 matic conditions during the ten months preceding the time of flower- 

 ing. (U. S. E. S. B. 178: Wis. E. S. B. 137.) 



