2.  The  amount  of  moisture  in  soil  is  of  the  utmost  importance,  for  the
supply  of  the  rootlets  of  trees.  There  is  a  vast  quantity  of  water  given
forth  through  the  leaves  during  the  annual  period  of  vegetation.  The
soil  must,  therefore,  be  able  to  absorb  and  retain  moisture.  Loose  sand,
■with  a  small  percentage  of  clay,  absorbs  easily,  but  does  not  retain  it.
Binding  clay  absorbs  slowly  and  to  moderate  extent,  but  is  very  reten-
tive.   A  mixture  of  vegetable  mold  modifies  both  extremes.
There  are  five  degrees  of  moisture  in  soils :

(1)  Wet. — On  lifting  a  handful,  water  drops  to  the  ground.
(2)  Moist. — On  squeezing  a  handful,  water  drops  to  the  ground.
(3)  Fresh. — On  squeezing  a  handful,  traces  of  moisture  remain  on  the
hand.
(4)  Dry. — On  squeezing  a  handful,  no  traces  of  moisture  remain  on
the  hand.
(5)  Arid. — On  being  merely  rubbed,  it  flies  off  as  dust.
'6.  The  degree  of  looseness. — The  more  clay  there  is  in  soil  the  more
binding  it  is,  and  according  as  sand  or  lime  is  added  the  more  it  be-
comes loose.  Binding  clay  opposes  tree-growth,  by  not  allowing  the
free  entrance  of  moisture  and  air.  On  the  contrary,  very  loose  soils,
especially  if  shallow,  are  apt  to  become  dry,  and  are  exposed  to  tiie
influence  of  frosts,  while  trees  having  no  firm  support  in  the  shallow,
unretentive  soil  often  fall  in  storms.  Here,  again,  both  extremes  are
modified  by  an  admixture  of  humus.
