 Some of the greatest imports to Plymouth from the Americas and Europe during the latter half of the 19th century included maize , wheat , barley , sugar cane , guano , sodium nitrate and phosphate Aside from the dockyard in the town of Devonport , industries in Plymouth such as the gasworks , the railways and tramways and a number of small chemical works had begun to develop in the 19th century , continuing into the 20th century . 
