(1) From the analysis of stamens, the flowers of corn are unisexual flowers. The pollination method of corn in Figure 1 is cross-pollination. Cross-pollination is often restricted by environmental conditions, and there is no opportunity for pollination. For example, there is no wind for wind-pollination, and insect-pollination is due to strong winds or low temperatures, and there is a lack of enough insects to fly out for active pollination, etc., thus reducing pollination and fertilization. opportunities, affecting fruit and seed yields. In agricultural production, artificial assisted pollination is often used to overcome the shortcomings of insufficient pollination due to insufficient conditions and to achieve the expected yield. The specific method of artificial assisted pollination is not exactly the same for different crops. Generally, pollen is collected from the stamens first, and then the pollen is smeared or sprinkled on the stigma of the plant's pistil, or the collected pollen is mixed under low temperature and dry conditions. Store for later use. Therefore, artificial assisted pollination can increase the yield of corn, sunflower, etc., and make up for the lack of cross-pollination in natural conditions.
(2) When a flower completes pollination and fertilization, the ovary develops into fruits and the ovules develop into seeds. Therefore, the number of fruits depends on the number of ovaries. One fruit requires one pollen grain. If there are 198 corn grains on the corn ear, at least 198 pollen grains are needed. Since corn is a fruit, each corn kernel develops from an ovary.
(3) a is the stem of corn, which develops from the 2 germs in Figure 2; the structure of corn seeds includes pericarp and seed coat, endosperm and embryo. Nutrients are stored in the endosperm.
(4) We know that when a seed germinates, the embryo absorbs the nutrients originally stored in the seed and develops into a seedling. At this time, the organic matter in the seed is reduced. When the seedlings emerge from the soil and can carry out photosynthesis, the nutrients in the plants will gradually increase, causing the plants to grow up.
So the answer is: (1) Parthenocarpic cross-pollination and artificial pollination (2) 198? ovary
(3) 2? germ and 5 endosperm
(4) Decrease first, then increase