126  The  Tubers  of  Dioscorea  Species.  {^VarotiSSf™' 
fall,  I  was  surprised  at  the  appearance  of  stems  and  leaves  in  1888, 
and  annually  since  then,  proving  that  the  root  would  survive  our 
winters.  During  the  past  summer  the  plant  grew  in  a  sunny  posi- 
tion, attained  a  considerable  height,  and  produced  flowers  and  many 
axillary  tubers,  which  were  subjected  to  analysis  by  Mr.  Meink. 
Most  of  the  leaves,  particularly  on  the  upper  branches,  were  oppo- 
site or  in  whorls  and  the  plant  could  therefore  not  be  the  one  named 
above,  which  has  the  leaves  never  opposite ;  Mr.  Thos.  Meehan 
kindly  identified  the  plant,  and  confirmed  the  opinion  that  it  is 
merely  the  Chinese  yam,  Dioscorea  glabra,  Roxburgh,  or  D.  Batatas, 
Decaisne,  which  was  brought  to  the  notice  of  the  French  Academy 
nearly  forty  years  ago  as  a  valuable  food  plant  by  Decaisne. 
The  genus  Dioscorea  comprises  about  1 50  species,  nearly  all  of 
them  confined  to  tropical  or  subtropical  countries.  A  number  of 
these  species  have  large  tuberous  roots,  which  on  account  of  the 
starch  present  in  them  are  used  as  food,  and  are  generally  known  as 
yam ;  the  tubers  growing  in  the  axils  of  the  leaves  of  some  species, 
it  appears,  may  likewise  be  utilized.  But  many  of  these  products 
in  their  natural  state  are  bitter  or  acrid,  and  are  known  to  possess 
poisonous  properties,  which,  however,  are  removed  by  washing  with 
water,  or  with  alkalies,  or  by  boiling  or  roasting. 
Messrs.  Heckel  and  Schlagdenhauffen  have  recently  made  a  study 
[Revue  des  Sciences  natur.  appl.,  March,  1892)  of  the  tubers  of 
Dioscorea  bulbifera,  Linne,  and  ascertained  that  in  the  Gaboon 
country  of  tropical  Africa,  the  aerial  tubers  are  looked  upon  as 
being  decidedly  poisonous,  while  in  other  French  colonies  they  are 
considered  inoffensive.  Working  with  the  aerial  tubers  procured 
from  the  Gaboon  country,  they  separated  with  petroleum  benzin 
some  wax  and  chlorophyll,  and  then  exhausted  the  residue  with 
alcohol ;  this  extract  on  being  treated  with  water  left  some  resin 
behind,  while  yellow  coloring  matter,  saccahrose  and  a  bitter  prin- 
ciple went  into  solution ;  this  solution  injected  subcutaneously  proved 
poisonous  to  frogs  and  was  shown  to  contain  a  glucoside.  The 
authors  found  the  underground  tubers  to  be  entirely  free  from  this 
toxic  principle. 
It  is  of  interest  to  note  the  fact  that  Mr.  Meink's  investigation 
has  also  shown  the  presence  of  a  glucoside  in  the  aerial  tubers  of 
the  Chinese  yam,  and  it  remains  to  be  determined  whether  it  also 
possesses  poisonous  properties.    With  the  exception  of  the  two 
