34         RESEARCHES  ON  THE   RESPIRATION   OF  FLOWERS. 
absorbed  atmospheric  oxygen  more  rapidly  ;  but  later  and  mul- 
tiplied experiments  on  various  flowers  have  shown  me  that  this 
view  could  not  be  established  as  a  general  conclusion. 
On  the  other  hand,  I  am  convinced  that,  other  things  being 
equal,  though  the  proportion  of  carbonic  acid  formed  is  gene- 
rally rather  greater  when  the  flower  is  exposed  to  the  light  than 
when  it  is  in  perfect  darkness,  the  difference  is  far  from  being  so 
great  as  is  supposed.  This  difference  becomes  much  more  ma- 
nifest when  the  normal  air  is  replaced  by  pure  oxygen. 
When  the  phenomenon  takes  place  in  ordinary  air,  it  is  not 
unusual  to  find  that  the  results  are  the  same,  whether  obtained 
in  darkness  or  in  a  bright  light.  This  result  is  very  different 
to  those  obtained  with  most  organic  substances,  which,  enclosed 
in  equal  weights  in  tubes  containing  equal  volumes  of  atmo- 
spheric air,  consume  much  more  oxygen  in  light  than  in  dark- 
ness. The  differences  observable  under  these  circumstances 
may  probably  be  accounted  for,  in  the  one  case,  by  the  bodies 
undergoing  change  being  possessed  of  more  or  less  energetic 
vitality,  and  in  the  other  being  entirely  inert. 
In  operating  on  the  same  plant,  either  in  complete  darkness 
or  in  the  light,  it  is  found  that  as  the  temperature  is  raised, 
the  proportion  of  carbonic  acid  produced  in  a  given  time  is  very 
appreciably  augmented.  This  result  is  observable  in  the  most 
various  flowers.  When  the  outer  temperature  varies  from  -f 
15  to  +  25°,  the  transformation  of  oxygen  into  carbonic  acid 
is  rapid;  but  with  temperatures  between  -f  5  and  +  ifc  is> 
on  the  contrary,  slow. 
The  plant  does  not  consume  the  same  quantity  of  oxygen  at 
different  periods  of  its  development,  nor  produce  the  same  pro- 
portion of  carbonic  acid.  Such  is  the  result  of  a  large  number 
of  comparative  experiments.  The  differences  are,  nevertheless, 
not  very  considerable.  By  gathering  from  the  same  plant  ex- 
actly equal  weights  of  buds  and  full-blown  flowers,  and  placing 
them  respectively  in  equal  volumes  of  normal  air  under  identical 
conditions  of  light  and  temperature,  *the  consumption  of  oxygen 
is  almost  always  slightly  greater  with  the  buds  than  with  the  full- 
blown flowers, — a  result  which  is  not  surprising  when  we  consider 
that  the  vital  force  is  greater  in  the  first  than  in  the  second 
instance ;  still,  the  difference  is  never  very  striking. 
