Tulip, the spring-blooming ornamental flower famous for its dazzling beauty that usually grows in colder countries, is now laregly being cultivated commercially in Gazipur.   Tulip, the national flower of Turkey and the Netherlands, grows from bulbs. Most tulips thrive in colder winters because of the long-chilling requirement for bulbs.   The flower comes in many colours like orange, pink, cherry, magenta, salmon, crimson, purple, apricot, lilac, mauve, blue, yellow, apricot, violet, terracotta, red, scarlet, chocolate and brown along with many shades.   Delwar Hossain, 50, a farmer of Kewa village in Sreepur upazila, is cultivating the attractive flower in his garden which he named 'Moumita Flowers'.