I  have,  in  the  course  of  some  years,  treated  these  problems
from  different  points  of  view.  The  first  characters  which  I
found  related  to  the  development  of  spores,  with  especial
reference  to  the  cardinal  points  of  temperature.  It  is  now
generally  acknowledged  that  this  method  of  spore  analysis  is
of  importance,  and  on  this  basis  I  have  further  devised  the
above-mentioned  method  for  the  practical  examination  of
brewery  yeast.  I  therefore  still  lay  great  weight  on  these
characters  ;  but  I  have  never  held  the  opinion — as  often  stated
by  superficial  readers  of  my  writings — that  they  are,  in  them-
selves, sufficient  for  the  determination  of  all  species ;  on  the
contrary,  I  have  always  endeavoured  to  discover  new  distinc-
tive characters,  and  I  have  also  already  given  a  whole  series.
