THE  AMEEICAN 
Investigators  in  the  domain  of  agricultural  chemistry  have  de- 
voted a  greater  measure  of  attention  to  the  productiveness  of  the 
soil  than  has  been  given  to  the  chemical  composition  of  the  crops 
concerned.  From  this  generalization  we  must,  however,  except  to 
some  extent  those  workers  engaged  upon  the  study  of  sugar-produc- 
ing crops  by  whom  great  success  has  been  achieved  in  raising  the 
percentage  of  sugar  in  root  crops. 
In  the  case  of  medicinal  plants  there  is  much  need  for  investiga- 
tions of  this  character  and  this  need  is  rapidly  becoming  greater 
as  it  becomes  more  forcibly  understood  that  the  medicinal  value 
of  different  samples  of  the  same  drug  may  vary  enormously. 
It  is  this  latter  consideration  which  has  led  to  the  increasing  de- 
mand for  the  standardization  of  drugs  and  of  their  preparations,  an 
advance  for  which  pharmacy  owes  much  to  the  compilers  of  the 
eighth  revision  of  the  United  States  Pharmacopoeia. 
Whether  or  not  an  extension  of  our  knowledge  in  the  direction 
indicated  will  ever  render  it  possible  in  a  practical  way  to  control 
the  amount  of  active  principle  present  in  a  plant  grown  under  cultiva- 
tion, it  must  be  admitted  that  the  investigation  of  such  a  problem 
is  of  great  practical  importance  as  well  as  of  deep  scientific  interest. 
In  work  of  this  character  there  are  so  many  variable  factors 
concerned  that  before  generalizations  may  safely  be  considered,  we 
require  to  make  a  vast  accumulation  of  accurate  data,  and  such  ac- 
cumulated results  are  not  yet  available. 
(487) 
