at 512/A Russa Road, now known as 34/A Shyama Prasad Mukher jee Road, Calcutta, by a registered lease deed dated 26th September, 1946, hereinafter referred to as 'the lease ', at the first instance for a period of 10 years from 1st April, 1946 but if the lessee did not fail to pay the rent to the lessor and rates and taxes to the municipality during .that period, the lease would be extended for a further period of 5 years i.e. upto 31st March, 1961 at the rent of Rs.250 in place of Rs.200 per month; and if he continued to do like wise, it would be extended for a further period of 5 years, that is, upto 31st March, 1966, at a monthly rent of Rs.300 in place of Rs.250; and if he continued to do likewise, during the period of 20 years, he would be entitled to obtain extension for a further maximum period of one year at a rent of Rs.500 per month in place of Rs.300 per month.