A metro train is seen behind tulips in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)

Tulips are seen in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)

Tulips are seen in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)

A tourist takes photos in Emirgan park in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)

Tulips are seen in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)

Tourists take photos in front of the Festival billboards in Emirgan park in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)

People walk past tulips in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)

Tulips are seen in Istanbul, Turkey, April 8, 2014. The annual International Istanbul Tulip Festival took place from 6th to 30th of April, with 20 million tulips planted in Istanbul's parks. Tulip is the national flower of Turkey. (Xinhua/Lu Zhe)