CHAPTER XI. 



THE WATER OF SOILS. 



HYGROSCOPIC AND CAPILLARY MOISTURE. 



\YHEN it is remembered that from 65 to over 90^ of the 

 fresh substance of plants consists of water, the importance of an 

 adequate and regular supply of the same to growing plants is 

 readily understood. But it seems desirable, before discussing 

 the relations of water to the soil and to plant life, to consider 

 first the physical peculiarities which distinguish it from nearly 

 all other substances known. That it is colorless, tasteless, in- 

 odorous, and also chemically neutral, alone constitutes a group 

 of properties scarcely found in any other fluid. But its special 

 adaptation to its functions in relation to vegetable and animal 

 life are much more fundamental, as is shown in the table of its 

 physical constants as compared with other well-known sub- 

 stances, given below. 



PHYSICAL K.UT'ik-s <>! \VATKR COMPARED WITH OTHKR SCHSTANCKS (PER UNIT 



WEIGHT). 



Capillary as< ent in glass tubes 

 of one mm. diameter. 



Water 14 mm. 



AK ohol 6 mm. 



Olive oil i mm. 



1 1: \ i KM \TIONS. 

 Density. 



Water at o (". (freezing 



pt.) 99988 



Water at | i Maximum 



density) i.ooooo 



Water a't 15 C. (ordi- 

 nary temperature) . . . .990 



Ice at o" (freezing pt. i. .92800 



Specific lli-.it>. 



Water i.ooo 



li-e 502 



MI )- ; 



< 'lay. ( a.iss. . . .iSo-.2OO 



( 'hairoal 241 



Wood 032 



< Inld, Lead 032-.C-3I 



/.in i 096 



Steel 119 



Heat of fusion. 



Water (Ice). .. So Cal. 



Metals 5-jS 



Salt-,, (itu 1. sili- 

 cates) 40-63 " 



Heat i>f Kvaporation. 



Water al -<> .613 Cal. 

 " 100 ('.637 " 



\1< oho] 209 " 



Spirits of Tur- 

 pentine 67 " 



Summarizing the meaning of the data given in the above 

 table with respect to organic life. \\ e see, first, that \\ater rises 

 higher both in the soil and in the tissues of the plant than any 



1 88 



