grass.dat:
Linthurst, R.A. (1979) "Aeration, nitrogen, pH, and salinity as factors
affecting Spartina alerniflora growth and dieback" Ph.D. thesis. North
Carolina State University.
Contains data
  Obs: 45
 Vars: 6
  1. bio    biomass i(gm per square meter)
  2. sal    salinity (parts per thousand) 
  3. K      potassium (parts per million)
  4. Na     sodium (parts per million)
  5. Zn     zink (parts per million)

Each group of 5 is from the same location/type combination