potato vs sweet potato

potato

noun
  • The tuber of a plant, Solanum tuberosum, eaten as a starchy vegetable, particularly in the Americas and Europe; this plant. 

  • Metaphor for a person or thing of little value. 

  • A camera that takes poor-quality pictures. 

  • A mentally handicapped person. 

  • A conspicuous hole in a sock or stocking. 

  • An underpowered computer or other device, especially when small in size. 

adj
  • Underpowered; low-end. 

sweet potato

noun
  • The tuber of this plant cooked as a vegetable. 

  • An ocarina. 

  • A tropical perennial American vine, Ipomoea batatas, having a fleshy tuber. 

How often have the words potato and sweet potato occurred in a corpus of books? (source: Google Ngram Viewer )