原因是
松果在天气热的时候，会散开鳞片，让种子可以从中落到地上，生根发芽。天气冷的时候，松果为保护种子避免被冻坏，会收拢鳞片，同时天气冷也不适宜种子生根发芽。而且，松果即使已经掉到地上，也可以根据天气冷热，张开或收拢鳞片。
Background
Did you know that pinecones can stay on pine trees for more than 10 years before falling to the ground? During that time seeds for new pine trees grow under the scales of the pinecones. The scales protect the seeds from bad weather—and hungry animals. Eventually, however, the seeds need to be released so that they can grow into new trees. To make sure they have the best chance of finding fertile soil and growing into trees, the pinecone scales stay tightly closed when the weather is inhospitable to new seed growth—that is, when it’s very cold and damp outside. In contrast, when the weather is hot and dry, the seeds will have an easier time finding good soil for growing into trees. In these conditions the pinecone scales will open, allowing seeds to escape and drift away to find new ground to grow into new trees!
As you will observe in this activity, after pinecones fall from the tree they can still open and close; we will test the conditions that cause this—all from home!