law: Transfer of Property Act, 1882
  70. Accession to mortgaged property
  If, after the date of a mortgage, any accession is made to the
  
  mortgaged property, the mortgagee, in the absence of a contract to the
  
  contrary, shall, for the purposes of the security, be entitled to such
  
  accession.
  Illustrations
  (a) A mortgages to B a certain field bordering on a river. The
  
  field is increased by alluvion. For the purposes of his security, B is entitled
  
  to the increase.
  (b) A mortgages a certain plot of building land to B and
  
  afterwards erects a house on the plot. For the purposes of his security, B is
  
  entitled to the house as well as the. plot.