4H 
Plant  Morphology  and  Taxonomy. 
(  Ana.  Jour  Pharm. 
I  September,  1905. 
While  species  are  considered  to  be  the  true  units  in  organic  life, 
there  is  still  much  uncertainty  as  to  what  constitutes  a  species,  as 
already  indicated,  and,  furthermore,  it  has  been  shown  on  experimen- 
tal grounds  that  many  systematic  species,  as  they  are  accepted 
nowadays,  are  as  a  rule  compound  groups.  Sometimes  they  consist 
of  two  or  three,  or  a  few  elementary  types,  but  in  other  cases  they 
comprise  twenty,  or  fifty,  or  even  hundreds  of  constant  and  well 
differentiated  forms."  It  is  interesting  to  note  in  this  connection 
that  while  Linnaeus  held  to  the  view  that  species  were  distinct  crea- 
tions, he  nevertheless  recognized  the  compound  nature  of  the  then 
existing  species. 
According  to  De  Vries  the  real  units  are  the  elementary  species ; 
their  limits  often  apparently  overlap  and  can  only  in  rare  cases  be 
determined  on  the  sole  ground  of  field  observations.  He  then  goes 
on  to  say  that  pedigree-culture  is  the  method  required  and  that  any 
form  which  remains  constant  and  distinct  from  its  allies  in  the  garden 
is  to  be  considered  as  an  elementary  species. 
To  obviate  the  difficulties  which  would  arise  from  the  multiplica- 
tion of  species,  their  numbers  being  already  cumbersome,  De  Vries 
suggests  the  recognition  of  two  sorts  of  species.  He  says :  "  The 
systematic  species  are  the  practical  units  of  the  systematists  and 
florists,  and  all  friends  of  wild  nature  should  do  their  utmost  to  pre- 
serve them  as  Linnaeus  proposed  them."  On  the  other  hand,  he 
maintains  that  "  both  for  the  theory  of  descent  and  for  our  concep- 
tion of  systematic  affinities  at  large,"  a  study  of  elementary  species  is 
essential.  "  For  it  is  obvious  that  they  only  can  be  observed  to 
originate,  and  that  the  systematic  species,  because  they  are  only 
artificial  groups  of  lower  unities,  can  never  become  the  subject  of 
successful  experimental  inquiry." 
For  some  time  past,  in  the  study  of  certain  of  the  cryptogams,  as 
bacteria,  yeasts  and  fungi,  there  has  been  a  disposition  to  rely  upon 
physiological  rather  than  morphological  characters,  this  being  due  not 
only  to  the  fact  that  these  are  more  constant  and  characteristic  in  these 
organisms,  but  also  to  the  fact  that  distinct  morphological  charac- 
ters are  entirely  wanting  in  some  cases.  While  the  necessity  for 
this  additional  study  in  the  higher  plants  is  not  so  apparent  on 
account  of  the  presence  of  well-defined  morphological  characters,  still 
the  value  of  physiological  marks  as  one  of  the  bases  of  classification 
