48  Mr.  hunter  on  the  Heat,  See. 
from  the  fap,  the  heat  could  be  very  little,  efpecially  as 
the  gimlet  was  not  in  the  leaf:  heated  by  the  operation. 
4tll. 
Car.  poplar, 
17* 
Eng.  poplar, 
17 
Ori.  plane, 
1 7 
Occ.  plane, 
17 
Carol,  plane, 
17 
Birch, 
17 
Scotch  fir, 
16^ 
It  will  be  neceflary  to  obferve,  that  the  fap  of  the 
walnut  tree,  which  flowed  out  in  great  quantity,  froze 
at  3 i°.  I did  not  try  to  freeze  the  fap  of  the  others. 
Now,  fince  the  fap  of  a tree,  when  taken  out,  freezes 
at  320;  alfo,  fince  the  fap  of  the  tree,  when  taken  out 
of  its  proper  canals,  freezes  when  the  heat  of  the  tree  is 
at  3 1° ; and  fince  the  heat  ofrfhe  tree  can  be  fo  low  as 
170  without  freezing ; by  what  power  are  the  juices  of 
the  tree,  when  in  their  proper  canals,  kept  fluid  in  fuch 
a cold  ? Is  it  the  principle  of  vegetation  ? Or  is  the  fap  in- 
clofed  in  fuch  a way  as  that  the  procefs  of  freezing  can- 
not take  place,  which  we  find  to  be  the  cafe  when  water 
is  confined  in  globular  veflels?  If  fo,  its  confinement 
rauft  be  very  different  from  the  confinement  of  the 
moiflure  in  dead  vegetables;  but  the  circumftance  of 
vege- 
