PLANT PHYSIOLOGY AS RELATED TO PRUNING 



constant supply of water during its growing season, the 

 soil, however rich in plant food, might as well be sterile. 

 Succulent plants and plant tissues in active growth con- 

 tain relatively little fiber, mineral and other solid material, 

 but 75 per cent or more of water. 

 Thick-walled, protective and woody 

 tissues contain relatively less, as 

 may also the succulent parts during 

 periods of drouths. 



8. Dual function of water. Water 

 acts in the double capacity of (1) a 

 plant food solvent and transporting 

 agent, and (2) a crude plant food 

 itself, as in the manufacture of 

 starches, sugars, cellulose, etc. Dur- 

 ing the growing period, therefore, 

 ordinary plants must be in constant 

 touch with water in greater or lesser 

 supply. Their forms, functions and 

 development are also affected by the 

 volume, the distribution and the min- 

 eral content of the available water. 



Water maintains rigidity in succulent plants and in 

 those growing parts whose cells have not become firm 

 enough to maintain their normal form when the supply 

 of water becomes reduced. This function produces what 

 is termed hydrostatic rigidity, since it enables succulent 

 plants to support considerable weights of branches and 

 other plant parts. Should the water supply become re- 

 duced, such plants would droop or wilt more or less seri- 

 ously. Hence, ample water is a prime requisite of suc- 

 cessful development. The supply may be reduced by 

 other means than simply lack of water in the soil. 



"Booth reports an instance in which peaches on Marianna plum 

 stocks grew fairly' well for two years, though from the start the 

 peaches grew more rapidly than the plums, so the peach trunks were 

 at two years twice as large at the union as below. During the 

 second season the weather was very hot and dry, and the peach trees, 



FIG. 6 



CHLORENCHYMA CELL 

 SHOWING STARCH 



GRAINS AND 

 CHLOROPLASTS 



