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Charles  Darwin. 
Am.  Jour.  Pharm. 
July,  1909. 
During  many  years  Professor  Asa  Gray  of  Harvard  University 
maintained  an  active  correspondence  with  Darwin,  who  was  enabled 
to  secure  and  observe  a  number  of  American  plants  of  striking 
ecologic  type.  Stimulated  to  inquiry  by  a  paper  of  Prof.  Gray's 
on  the  movements  of  the  tendrils  of  some  cucurbitaceous  plants, 
Darwin  undertook  the  study  of  over  100  widely  distinct  species  of 
climbing  plants  which  presented  sufficient  novelty  to  justify  him 
in  publishing  his  book  of  208  pages  entitled  "  The  Movements  and 
Habits  of  Climbing  Plants,"  which  appeared  in  1876.  His  study 
led  him  to  divide  them  into  four  classes :  first,  those  which  twine 
spirally  round  a  support,  and  are  not  aided  by  any  other  movement ; 
second,  those  endowed  with  irritable  organs,  which  when  they 
touch  any  object  clasp  it;  such  organs  consisting  of  modified  leaves, 
branches,  or  flower  peduncles.  Plants  of  the  third  class  ascend  by 
the  aid  of  hooks,  and  those  of  the  fourth  by  rootlets.  As  to  the 
evolution  of  the  climbing  habit  Darwin  concludes  that  leaf  climbers 
were  primordially  twiners  and  tendril  bearers  (when  formed  of 
modified  leaves)  were  primordially  leaf  climbers. 
A  typic  flower  has  a  pistil  surrounded  by  a  row  of  stamens 
so  that  it  would  seem  at  first  sight  easy  for  the  pollen  to  fall  on 
the  stigma.  Such  self-pollination  does  happen,  but  in  the  majority 
of  flowers  there  are  three  principal  modes  by  which  self-fertilization 
is  presented.  First,  in  many  species  the  stamens  and  pistils  are 
situated  in  different  flowers ;  such  species  are  called  diclinous,  which 
is  either  monoecious  with  the  distinct  flowers  on  the  same  plant  or 
dioecious  on  different  plants.  Second,  Sprengel  discovered  dichog- 
amy where  the  pistil  and  stamens  mature  at  different  times  so 
that,  as  in  Arum,  when  the  pistil  matures  before  the  anthers  these 
plants  are  proterogynous,  when  the  anther  matures  before  the  pistil 
proterandrous.  Darwin  discovered  the  third  method  in  the  presence 
of  two  or  more  kinds  of  flowers  (heteromorphism)  on  the  same 
species  differing  in  the  relative  position  of  the  stamens  and  the 
pistil  which  are  so  placed  as  to  favor  the  transference  by  insects 
of  the  pollen  from,  the  anther  of  the  one  form  to  the  pistil  of  the 
other.  Plants  with  two  kinds  of  flowers  are  called  dimorphic,  those 
with  three  kinds  trimorphic.  The  results  of  these  studies  were 
incorporated  in  a  volume  entitled  "  Different  Forms  of  Flowers  on 
Plants  of  the  Same  Species,"  1877,  dedicated  to  Professor  Asa 
Gray  as  a  small  tribute  of  respect  and  affection. 
The  last  volume  by  Darwin  of  a  botanic  character  was  one 
