494 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



1. Excessive or strong vegetative growth, 

 especially in young' trees just coming into 

 bearing. Such trees usually set light 

 crops and the fruits are abnormal in size. 

 Fruits borne far out on the terminals 

 are very liable to water core, whether 

 the trees are old or young, providing the 

 trees are vigorous. Trees making poor 

 growth, which may be caused by soil 

 conditions, lack of moisture, root trouble, 

 or any other cause, rarely show water 

 core in the fruit. 



2. High cultivation is a factor, but 

 alone would not cause the trouble. How- 

 ever, well cultivated soils retain moisture 

 much better than those which are not 

 cultivated, hence, as a rule, high cultiva- 

 tion will promote vigorous growth and, 

 therefore, favors water core, providing 

 other factors are present. 



3. Excessive precipitation or Irrigation 

 shortly before the maturity of the fruit 

 if followed by great extremes of temper- 

 ature and atmospheric humidity, are fac- 

 tors of the greatest importance. During 

 hours of sunshine the moist ground is 

 warmed to such an extent that water is 

 readily taken up by the root system, and 

 at this time transpiration is also very 

 rapid. During the night the atmospheric 

 temperature lowers to the point of satura- 

 tion, this often being very little above the 

 freezing point; however, the moist soil in 

 which the roots are growing remains 

 warm, or at least several degrees above 

 that of the air temperature. Under such 

 conditions, sap pressure is continuous, 

 but transpiration is checked. Evapora- 

 tion cannot take place from any surface 

 when the surrounding medium (air, in 

 this case) has reached the point of sat- 

 uration. With transpiration checked and 

 the sap pressure continuing, the tissues 

 along the lines of greatest pressure 

 must give way. These tissues are 

 found in the fruits, especially those 

 farthest out on the terminals, because 

 they are exposed to extremes of temper- 

 ature. Fruits on the south or southwest 

 sides of trees are always most affected. 



4. Severe pruning shortly before the 

 ripening period, or defoliation by disease 

 or otherwise, thus causing the fruit to be 

 exposed as well as reducing the evapora- 



tion surface of the tree, will have a 

 tendency to produce water core. 



5. Frosts, which are severe enough to 

 injure the foliage, have an effect similar 

 to that of defoliation, since leaves which 

 are so injured no longer function as true 

 agents of transpiration. Certain chemi- 

 cal activities are also set up in plants 

 after frosts have injured them, and this 

 produces rapid ripening in the case of 

 apples. It is quite noticeable after a 

 heavy frost that apples color rapidly, this 

 being due to the formation and activity 

 of certain enzymes. 



6. Cell tension or turgor may be in- 

 duced by the rapid conversion of starch 

 into sugar. This tension may be caused 

 in two ways: (1) by the rapid absorp- 

 tion of water by the sugar through os- 

 motic pressure; (2) by the rearrange- 

 ment of the molecules during the process 

 of starch conversion into sugar. This, 

 however, is of less importance than the 

 other factors enumerated above. 



Weather conditions favored water core 

 during the season of 1912 in the Rogue 

 River district. During this period prac- 

 tically clear weather prevailed. Begin- 

 ning with August 31 and ending Septem- 

 ber 8, 1.15 inches of rain fell. Following 

 this period of moderate temperatures 

 came three weeks of clear weather with 

 high temperatures during the hours of 

 sunshine and low temperatures during 

 the nights. 



A careful examination of orchards of 

 the same age and variety showed that 

 the amount of water core present in the 

 fruit was in direct proportion to the 

 amount of precipitation or irrigation, 

 range in temperature and range in rela- 

 tive humidity. Records were taken on 

 the valley floor where the range in both 

 temperature and relative humidity was 

 very great. At elevations where this 

 range was not so great, there was very 

 little water core. The amount of pre- 

 cipitation also had its effect. In orchards 

 where the precipitation was light, water 

 core was much less abundant. A case 

 was noted where the rainfall was sup- 

 plemented by a heavy irrigation, both pre- 

 ceding and after the rain occurred. In 

 this orchard over 90 per cent of the fruit 



