Some of the main sources of pollen are trees in the summer, grasses in the spring, and weeds in the winter.

The statement is false because it incorrectly categorizes the seasonal sources of pollen. In reality, trees are primary sources of pollen in the spring, not summer. Grasses typically pollinate during late spring and into early summer, while weeds are major contributors of pollen in the late summer and fall. The seasons in which these plants release pollen are important for understanding allergy seasons and environmental health, as different plants contribute to pollen counts at different times of the year. Therefore, the correct classification of pollen sources is crucial for accurate information regarding allergenic responses and public health advisories related to seasonal allergies.