|Sea squill (Drimia maritima)|
How does the hatsav know when August has arrived? It knows this because of the lengthening nights. The sea squill is what's known in scientific terms as a "short day" plant, which is a misnomer, as they are actually "long night" plants. "Short day" plants like sea squill and tobacco flower when the length of the night surpasses a threshold specific for that plant. This is as opposed to "long day" plants like carnations and oats, which flower when the night gets shorter than a set threshold.
Plants "know how long the night is thanks to a group of photoreceptors called phytochromes. In a simple model, phytochromes are activated by red light, and are turned on in the morning; they are deactivated by far-red light, the long waves at the end of sunset, so are turned off as night begins. Plants measure the time the phytochromes are turned off, and use this information to determine season.
|Sea squill leaves in winter|
Getting back to the seq squill, its floral stalk has no leaves, so where does this plant get energy from photosynthesis? The sea squill has two different life cycles. In the summer and fall, it flowers, but in the winter, when there's pleanty of water for to support photosynthesis and growth it produces large green leaves. Theses leaves produce the sugars that are stored underground in a large bulb. As the dry season starts these leaves wilt and dry up. But the bulb uses these stored sugars as energy to produce the flowering stalk in August.