Agriculture was carried on by peasants living in villages. The first ruler credited with digging canals for promoting agriculture was the immigrant 'Qarauna' sultan, Ghiyasuddin Tughluq. It was under Flruz Tughluq in the period 1351-86 that the biggest network of canals known in India until the nineteenth century was created. The peasants of the Delhi sultanate cultivated a very large number of crops. The fourteenth and fifteenth centuries saw the introduction of sericulture, or the breeding of the mulberry silkworm for producing true silk. In the western Panjab, which had seen two centuries of Ghaznavid rule, the Islamic taxation system was in operation. Barani introduces a new relationship in medieval economy: the relationship between land revenue and agricultural production. The iqtā's were the main instrument for transferring agrarian surplus to the ruling class and its soldiery. Another form of transfer of revenue claims existed, which went largely to maintain the religious intelligentsia and other dependants of the ruling class.