RAINFALL AND SOIL MOLSTURE 17 



two weeks after the latter rain before the moisture at 15 cm. had 

 been raised to 13 %, and four weeks after before it had l^een 

 raised to 16 %. As a result of another Hght rain of 0.15 in. on 

 November 26 the moisture at 15 cm. was maintained at 15 %, 

 until December 19. Other cases may be found by inspection of 

 the diagram in whicli the influence of heavy rains is felt imme- 

 diately at 3 cm. l)ut is registered at 15 cm. only after one or two 

 weeks. 



A long period of progressive desiccation of the soil which oc- 

 curred from November 26 to January 10 (see also fig. 1) was sud- 

 denly terminated on the latter date by a rain of 0.77 in. followed 

 on the succeeding days by rains of 0.18 in. and 0.02 in., which 

 resulted in a rise of the moisture at 3 cm. from 8 % on January 

 9 to 19 % on January 16; and at 15 cm. a rise from 14 % to 22 %; 

 at the same time that the soil at 30 cm. was unchanged at 

 15 %, although it rose to 19 % on January 23. 



The long rainless period from April 2 to July 1 was accompanied 

 by a slow desiccation, in which the soil at 3 cm. remained at 

 about 2 %, that at 15 cm. fell from 14 % to 7 %, and that at 30 

 cm. from 15 % and 16 % to 9% and 10 %. The rise of moisture 

 at the lower depth on dates in June, when there was no rainfall, 

 may be due merely to the variation of the moisture in the places 

 at which samples were taken, or it may be due to the capil- 

 lary rise of water from lower bodies of soil which had remained 

 at a higher moisture. The rain of 0.98 in. which ushered in the 

 summer rainy season on July 1 raised the moistures on July 4 to 

 18 % at 3 cm. and 11 % at 15 cm., but did not affect the moisture 

 at 30 cm. so quickly. 



An unbroken continuation of the soil records became impossible 

 after July 4, but a series of three weekly sets of readings was 

 taken in August, 1911, after the summer rains had had an oppor- 

 tunity to replenish the soil moisture. There were several light 

 rains in July, terminating on July 25 in a rain of 0.33 in. There 

 then followed a period of 18 days without rain (see fig. 1). On the 

 thirteenth day of this dry period— August 7 — the moisture of the 

 soil at the three depths was respectively 3 %, 13 % and 16 %. 

 On August 13 the dry period was terminated by a rain of 0.30 



THE PLANT WORLD, VOL. 17, NO. 1, 1914 



