1. We accept the finding of the Lower Appellate Court that Exhibit II is not binding on the plaintiffs, nor do we see any reason for differing from its conclusion that the defendants have not proved any circumstances which could be held to estop the plaintiffs from setting up the invalidity of Exhibit III as against them. One further contention remains to be dealt with, namely, that the plaintiffs are not entitled to purapad or rent for more than six years before the date of the suit. The facts which lead to this contention are that the Karipanayam deed Exhibit I dated 1867) as modified by the documents of further charge (Exhibit II dated the 1st May 1876 and Exhibit III dated the 14th July 1881) provides that the mortgagee should deliver the 200 paras of paddy a year to the plaintiffs, that no paddy was delivered subsequent to the Karar (Exhibit XII dated the 4th March 1889), and that the plaintiffs, in consequence, claim to be entitled to have credit for all the rent due under the mortgages at the taking of account for the purposes of redemption. The Lower Courts have awarded the plaintiffs rent due after the death of Rama Pattar, the executant of Exhibit XII who was auth