564 FUNDAMENTALS OF FRUIT PRODUCTION 



shown elsewhere to be rather sensitive to temperature conditions during 

 the growing season. In other words, nearly all the available data con- 

 cern plants or situations such that the difference between heat required 

 and heat available is small. The grape in the northeastern states is 

 near the limit of its summer heat requirements; the pear and the apple 

 are not. 



The evident readiness of European authorities to recognize small 

 differences in ripening according to the stocks used and the preponderance 

 of American opinion — aside from a few instances — to the contrary can be 

 reconciled if the climatic differences are considered. Just as a few days of 

 unusual heat in the spring will force into simultaneous bloom varieties 

 that blossom at different times in a cooler season, the greater heat at 

 harvest in America probably obscures small differences that would be 

 apparent in a cool region or in a cool season. 



End-season Effects. Maturity of Wood. — Evidence of the effect of the 

 stock on the maturity of the wood, on the contrary, seems brought out 

 more clearly in America than in Europe because of the different winter 

 climates and the intimate relation of maturity to hardiness. There is, 

 however, some mention of these effects in parts of France. Baco reports 

 considerable difference in the time of ripening of the wood in grapes, 

 stating: "In recapitulation, the grafted vines ripened their canes less 

 than vines on their own roots. In this respect many grafts have appeared 

 to us to be influenced by the stock about as they would be by nitrogen- 

 ous fertilizers or by a mellow deep and fertile soil if one had not grafted 

 them,"* Since these differences have most intimate relation to hardiness, 

 they are discussed under the effects of the stock on hardiness. 



The fall of leaves from a deciduous stock does not cause the fall of 

 leaves on an evergreen cion. Though the trifoliate orange is deciduous, 

 other varieties worked on it are not; though the quince is deciduous, a 

 grafted loquat top is evergreen. This holds true in other cases. How- 

 ever, despite this retention of foliage, it is probable that the deciduous 

 stock has some effect tending toward a partial dormancy. Evidence of 

 this lies in the smaller injury at a given temperature to orange on trifoliate 

 than on evergreen stocks and in the possibility of transplanting the 

 loquat on quince without "balling" of the roots, provided the leaves are 

 stripped, though this cannot be done if it is on its own roots. 



Spring Effects. — Returning, for the sake of completeness, to the effect 

 of stock on spring growth, the behavior of cherries on Chicksaw plum 

 may be cited as typical. The stock starts much earlier and throws out 

 leaves and shoots while the cherry grafts remain dormant until their 

 customary season of growth. "^^ However, Brown^^ recognizes a delay 

 in blossoming of plums and almonds on certain varieties of plums. He 

 states: "Blossoms appear on plums from 1 to 2 weeeks later than the 

 almond. Where the plum stock has been tried the delay has been about 



