Read the following passage and answer the question: Different plants bloom at different ages, and the season and time of flowering are different. Winter wheat is sown and germinated in autumn.

(1) It can be seen from the development of flowers that stamens are directly related to the formation of fruits and seeds, so the main structure in flowers is stamens.

(2) According to the passage, "Winter wheat is sown and germinated in autumn, and blooms and bears fruit in early summer of the following year. For this kind of plants, the low temperature in late autumn and early winter becomes a necessary condition for flowering; Under the condition of long sunshine, American tobacco can't bloom when the plant height is 3-5 m in summer, but it can bloom when the plant height is less than 1m when it grows in greenhouse in winter. " It can be known that the external conditions that affect flowering are mainly temperature and sunshine time.

(3) Because "winter wheat is sown and germinated in autumn, and blooms and bears fruit in early summer of the following year, low temperature in late autumn and early winter becomes a necessary condition for this kind of plants to blossom", if winter wheat is replanted in spring, it will only grow seedlings without flowering and bearing fruit without low temperature treatment in late autumn and early winter.

(4) The six organs of plants are roots, stems, leaves, flowers, fruits and seeds. The "wheat grain" sown is actually a fruit, which belongs to the structural organ. As we all know, fruit develops from ovary.

So the answer is: (1) Stamens are directly related to the formation of fruits and seeds.

(2) Temperature and sunshine time

(3) Low temperature treatment is not carried out in late autumn and early winter.

(4) organs; ovary