Transpiration and Water Movement 97 



to a marked degree. In fact, if the water-supply is not 

 abundant, a combination of these conditions may promptly 

 result in wilting. The water-loss is not necessarily pro- 

 portional to changes in conditions, since when transpira- 

 tion becomes excessive, concentration of the cell-sap and 

 the closure of the stomata exert, in many cases, a most 

 important inhibiting effect, which is, in a way, protective. 

 The soil factors indirectly important in transpiration 

 are water-supply and the strength or composition of the 

 soil solution. 



58. Effects of excessive evaporation. - The permanent 

 effects of an excessive loss of water vary with the type 

 of plant. Herbaceous annuals might quickly wilt and 

 dry up. Deciduous perennials might be promptly de- 

 foliated. Many trees will show this during a summer 

 drought, and if later wet weather prevails, there may be 

 an entirely new season of growth. It is then comparable 

 in effect to cold. Doubtless the excessive shedding of 

 young flower-buds or " squares ' of cotton is due to 

 changes of the water relation. In general, reduced water- 

 supply has a tendency to ripen up all parts, to mature 

 seeds early, and often a considerable effect upon the com- 

 position of the product. Seeds ripened in this way are 

 said to show the effects of immaturity, as shown later. 



/ / 



59. Guttation. - The elimination of water as liquid 

 may occur in certain plants when absorption is promoted 

 and transpiration checked. It consists in the forcible 

 excretion through certain stomata of water which may 

 collect as drops on the edges of the leaves or may stream 

 down the leaf blades. It is conveniently observed upon 

 young corn, blackberry, canna, and other plants. It may 



H 



