Chapter X — 199 — Loss and Retention 



effect of disease and the appHcation of sprays, dusts, and wax dips on the 

 rate of water loss from plants. 



Studies of the effect of nutrient deficiency (lack of N, P, and K) on 

 stomatal behavior of a number of plants, including bean, corn, and tobacco 

 have indicated that a disruption of the general metabolism of the plant is 

 reflected in sluggish stomatal response to changing environment. Sub- 

 normal stomatal behavior is accompanied by an increased water require- 

 ment and a decreased yield and size (Table 47) (Desai, 1937). This re- 

 sult is in agreement with observations that application of fertilizers to in- 

 fertile soils reduces the water requirements of plants growing on them 

 (Kiesselbach, 1916). 



Increased water requirements and rates of transpiration are usually 

 observed in plants suffering from fungus diseases. This is not always 

 true (Reed and Cooley, 1913), as the fungus may occasionally actually 

 obstruct water loss from the leaf. Frequently the effect of the fungus is 

 most strongly manifested through a disruption of the normal diurnal 

 transpiration curve (Graf-Marin, 1934; Yarwood, 1936; Gassner and 

 GoEZE, 1936; and Johnston, 1940). Rupture of the cuticle or altered 

 stomatal response may cause a greatly increased rate of transpiration, espe- 

 cially at night when the cuticular influence would normally be most mani- 

 fest, and the amount of water lost directly through the mycelium of the 

 fungus may be considerable. Alteration in permeability caused by secretory 

 products of the fungus has also been suggested as a cause of accelerated 

 water loss (Weaver, 1916). 



Although many conflicting results have been obtained on the effect of 

 insecticides on transpiration, it seems certain that insecticides may alter the 

 rate of transpiration, either mechanically or chemically. The mechanical 

 action may cause a reduction in transpiration through physical interference 

 with water vapor diffusion from the leaf, or it may cause an increase due 

 to the presence of minute dust particles wedging in the stomata preventing 

 closure. This latter effect was observed by Beasley (1942) when fine 

 inert dusts were applied to the stomatal bearing surfaces of leaves; night 

 water loss was increased. 



Chemically, the specific effects of the insecticides may alter the permea- 

 bility of the cuticle, or stomatal sensitivity. Copper sprays have been shown 

 to increase transpiration by increasing cuticular transpiration (Wilson and 

 Runnels, 1933 ; Krausche and Gilbert, 1937 ; Foster and Tatman, 

 1940) ; other investigators have been unable to find significant effects on 

 transpiration by treatment with Bordeaux sprays (Childers, 1936; Mil- 

 ler, 1938; Loustalot, 1944). 



Excessive water loss during transplanting and storage of nursery stock 

 coupled with the great reduction of absorbing roots left on the plant largely 

 determines the production of new roots and the plant's survival. Seven 

 common practices Hsted by Erickson (1945) are employed to keep the 

 water loss below the absorption. These are 1) hardening of the plants, 

 2) retention of as many roots as possible, 3) removal of part of the top, 

 4) avoidance of drying between digging and planting, 5) planting in moist 

 soil and watering immediately, 6) protection from wind and sunshine, and 

 7) planting during cool, humid weather. 



The work of Morris (1921), Neilson (1928, 1931), Tukey and 

 Brase (1931), and Maney (1931), has been particularly influential in 

 making commercially practicable the use of melted wax in the treatment 



