26. (1) The following income of an assessee shall be classified and computed under the head “Agricultural income”, namely:- (a) any income derived by the assessee which comes within the meaning of “agricultural income” as defined in section 2(1); (b) the excess amount referred to in section 19(17); (c) the excess amount referred to in section 19(19). (2) Agricultural income derived from the sale of tea grown and manufactured by the assessee shall be computed in the prescribed manner. (3) Where the Board, by notification in the official Gazette, so directs, agricultural income from the sale of rubber, tobacco, sugar or any other produce grown and manufactured by the assessee may be computed in the manner prescribed for the purpose.