Children know that tomatoes are vegetables in summer, but they are generally not seen in winter. Farmers' uncles cultivate tomatoes planted in greenhouses so that people can eat fresh tomatoes in winter. Although tomatoes in winter are red and big, they taste light, neither sour nor sweet, and are not as delicious as tomatoes in summer. This is because during the development of tomato fruit, leaves need enough sunlight to accumulate sugar and make the fruit sweet. In winter, tomatoes planted in greenhouses can get enough water and fertilizer, but they can't get so much sunshine in summer, so the sugar in the fruit can't reach so much in summer. Because tomatoes in winter have more water and less sugar, they are not as delicious as those in summer.