EXPERIMENTS  ON  THE  COMPOSITION  OF  WHEAT  GRAIN.  169 
will  be  found  to  consist  partly  of  hard,  horny,  subfcranslucent 
grains,  partly  of  softer  opaque  floury  grains,  and  partly  of  grains 
presenting  a  mixed  aspect.  I  have  specially  examined  two 
varieties  of  wheat,  and  the  proportions  of  the  three  sorts  of  grain 
which  my  samples  contain  are  given  here  in  percentages  : 
Hallett's  white  rough 
Spalding  red  wheat  (1864.)         chaffed  (1865.) 
Translucent    .        .    49  per  cent.         24  per  cent. 
Medium         .       .34       "  31  " 
Opaque  .       .17      "  45  " 
These  proportions  fluctuate,  however,  even  with  the  same 
variety  of  wheat  under  the  various  conditions  of  season,  maturity, 
when  cut,  etc.  It  is  not,  however,  these  proportions  that  I  wish 
to  discuss,  but  a  remarkable  difference  in  composition  between 
the  translucent  and  the  opaque  grains.  I  am  aware  that  previ- 
ous observers  have  detected  certain  chemical  differences  between 
the  poor  shrivelled  grains  and  the  full  plump  grains.  But  the 
grains  which  I  find  to  offer  a  most  striking  contrast  as  to  the 
proportions  of  their  most  important  constituent,  present  no  strik- 
ing contrast  in  size,  shape,  or  weight.  In  Hallett's  white  wheat9 
for  instance,  the  24  translucent  grains  weigh  19  grs. ;  the  45 
opaque  graius  weigh  34*2  grs.  Had  the  opaque  grains  been  of 
exactly  the  same  density  and  size  as  the  translucent  grains,  their 
weight  would  have  been  35*6  grs.  instead  of  34*2— a  very  trifling 
difference,  due  not  only  to  a  difference  in  the  size  of  the  two 
sorts  of  seed,  but  to  a  slight  difference  in  density  in  favor  of  the 
translucent  grains.  This  difference  in  density  is  brought  out 
very  plainly  when  the  seed  is  placed  in  a  strong  solution  of 
chloride  of  calcium  under  the  air-pump.  With  the  solution  of 
specific  gravity,  1*247,  71  per  cent,  of  the  grains  sink,  29  per 
cent,  float.  In  100  of  the  heavy  grains  thus  separated  there  are 
generally  35  to  38  translucent  grains,  and  only  18  opaque; 
while  in  100  of  the  light  grains  thus  separated,  there  are  usually 
only  10  translucent  grains,  and  as  many  as  70  opaque  grains. 
With  these  observations  on  one  physical  distinction  of  import- 
ance between  the  two  sorts  of  seed,  I  may  introduce  my  experi- 
ments on  their  chemical  differences. 
The  amount  of  water  in  the  selected  seeds  was  practically  the 
same  : — 
