49 



rROUGHT LIKIT . 



The drought iiait, or the per cent of n-ioistup^ in 

 th^ soil, whep pi«intt8 cease to secure sufficient Eoicture 

 for ^rovith, varies widely with the soil and to a i^^es d«jo;r«e 

 •Aith thtt plants, 



Th^ Euroau of Soils aonducted evaporfocion experiments 

 und9J- unifoi-n conditions upon different typee of soil. 

 The soils were artificiaiiy s«turat«>d and smail amounts were 

 u?ed. Ths ior.s m weignt was about uniform till the optirauja 

 ]r.oi£iur* WttS r-sached, wfter which there wi*s a progressive 

 de-crease in loss till the h3''groBcopic moisture was reached. 

 There a^-peisred to be no definite point at which the rat** of 

 ~vfiporation ehanged till the soil became axr dry. The 

 drought j-init, therefore, aprears to bfc '.'je rexation between 

 the neede of the plant and th*- progressively decreaaing 

 ability of the soil to supply raoisture, r£*th©r than any 

 definit* point at which the soil falls to .-^ive up reioisture. 



Nurs'irous determinations by King, Whitin^y^and others 

 show thy wide variation m the eapaeity of soils in the 

 fiyld to give up moistur« to plants, 



H^wa^rich (Physical Properties of Soiie 63, 64) deter- 

 ained the wilting point of plants in dlffer<^-nt BOils, 

 The plants wi^rfe grown in very small boxes till fully develop- 

 ed, and then piaeed under conditions of very little ©vapora- 



