68 



FUNDAMENTALS OF FRUIT PRODUCTION 



seasons that are cold and wet than during years of more nearly average 

 temperature and humidity. The decreased growth during the wet 

 season may be correlated with poorer aeration in the soil. 



Moisture Supply and the Growth Period in Early Spring. — Most 

 deciduous fruits have a short period of very rapid vegetative growth in the 

 spring, followed by a longer period of comparatively slow growth that 

 precedes the resting stage. That this is a characteristic of most deciduous 

 woody plants is brought out by data condensed in Table 34. Of the 

 70 species of trees, shrubs and vines considered hardy enough for outdoor 

 culture in central Michigan approximately one-fourth had completed 

 their shoot growth and formed their terminal buds by June 1, and over 

 two-thirds had reached a similar stage by June 20. In no case was there 

 appreciable shoot growth before May 1. Gourley^^ states that this 



Table 34. — Numbers of Trees, Shrubs and Vines Completing Shoot Growth 

 AT Different Dates 



(After Baileif) 



period of rapid growth in the apple lasts only about 25 days in New 

 Hampshire and that it is during this period that external factors, such 

 as moisture, have their greatest influence upon new tissue formation. 

 In his work approximately 43,000 measurements were taken and his 

 data point to the conclusion that there was no very close correlation 

 between the humidity and rainfall curves and the growth curve during 

 this period, though it was not possible to control all factors under field 

 conditions. The growth curve showed a closer correlation with tem- 

 perature than with any other factors studied. In Idaho, irrigation of 

 apple trees after July 15 had no effect upon shoot growth but as a rule 

 the more irrigation water applied before July 1, the greater was the shoot 

 growth. ^2* A similar correlation between growth and soil moisture 

 during the months of May, June and July has been observed in Indiana^^^ 

 and it was in the plots with the lowest water content that there was the 

 closest correlation between growth and soil moisture. With moisture 

 conditions approaching the optimum, an increased rainfall or surplus irri- 

 gation water has comparatively little influence in forcing growth. 



Pearson^^^ h^s made a valuable contribution to the knowledge of 

 the importance of an adequate soil moisture supply during the com- 



