^ptJember,%5.K}        P^nt  MorpJwlogy  and  Taxonomy.  4x3 
De  Vries,  on  the  other  hand,  as  a  result  of  his  own  experiments 
and  those  of  others,  claims  that  new  species  arise  by  discontinuous 
variations,  as  termed  by  Bateson,  or  by  mutations — that  is,  the 
sudden  appearance  of  new  characters — as  termed  by  De  Vries,  who 
even  goes  so  far  as  to  state  that  species  and  varieties  are  not  known  to 
originate  in  any  other  way  at  the  present  time.  De  Vries  considers 
that  there  are  periods  of  mutation  when  new  species  suddenly  make 
their  appearance,  or  the  type  may  remain  constant  for  many,  or  per- 
haps even  hundreds  of  years  without  the  appearance  of  a  new  species, 
although  it  is  claimed  that  the  periods  of  mutability  and  stability 
alternate  more  or  less  regularly. 
In  considering  the  subject  of  species  and  varieties  it  is  essen- 
tial to  make  a  clear  distinction  between  specific  and  varietal  marks, 
and  mere  individual  variations  or  fluctuations,  such  as  differences  in 
size,  color,  etc. 
The  true  significance  of  this  tendency  to  variation  on  the  part  of 
individual  plants,  while  better  understood  by  the  horticulturist  and 
experimental  morphologist,  is  not  always  appreciated  as  it  should 
be  by  the  systematist,  and  he  has  attached  more  importance  to  these 
fluctuations  than  he  should  have  done.  It  thus  comes  about  that 
frequently  transient  and  trifling  characters  are  made  the  basis  of 
taxonomic  work. 
While  I  have  no  intention  of  attempting  to  indicate  the  lines 
along  which  taxonomic  work  should  proceed,  I  may  be  permitted 
at  this  time  to  indicate  one  or  two  of  the  tendencies  which  are 
coming  to  the  front  in  the  determination  of  species.  De  Vries,  in 
his  recent  book  clearly  shows  what  is  meant  by  species  and  has  sug- 
gested a  way  by  which  we  may  determine  species  with  certainty. 
As  is  pretty  well  understood,  there  are  two  main  lines  of  organic 
evolution  at  large,  namely,  progression  and  retrogression.  With 
these  principles  in  mind  we  are  able  to  appreciate  what  constitutes 
a  new  species  or  variety.  When  a  species  arises  which  exhibits 
entirely  new  characters  or  characters  different  from  its  ancestors, 
and  remains  constant  for  some  years,  it  is  considered  to  be  a  new 
species.  When  a  species  shows  a  loss  of  some  usually  superficial 
character,  this  constitutes  a  variety,  or,  more  properly,  a  retrograde 
variety.  A  species  which  has  acquired  some  characteristic  of  an 
allied  form  likewise  constitutes  a  variety. 
