Plants, like animals, experience circadian rhythms. These are daily cycles that will do things like fluctuate the concentration of a particular hormone based on the time of day. Now these cycles are maintained and generated internally by what you could think of as a biological clock. However, they can be influenced by the external environment, and plants can have their circadian rhythms influenced by these things called cryptochromes. Now, these are photoreceptors that detect blue light and can have an influence on, for example, the turgidity of the plant in response to daylight.
Now, this plant over on the left, as you can see, is perked up, its leaves are open, and it's ready to absorb sunlight. This is going to be its, oops, its daytime condition. At night, the plant will lose turgidity and get droopy. Its leaves will close up, and it will not be in a prime position to absorb sunlight. However, it will give the plant certain other advantages. So this fluctuation over the day-night cycle will allow the plant to maximize its photosynthesis, and also, you know, do things like help protect it from environmental conditions by folding in at night.
Now some plants actually bloom in response to seasonal changes, and they detect this by sensing the lengths of the day-night cycle. Now we call these physiological responses photoperiodism. And some plants are considered long-day plants. These are going to be plants that bloom when the days are longest, which is going to be during the summer. Some plants are called short-day plants because they bloom when the days are shorter, and the days are going to be shorter during the spring and late summer or fall. Now, obviously, the days are going to be shortest in winter, but hopefully, you realize why it's not a great time for plants to be blooming. However, that cold does have an effect on plants' ability to bloom, some plants that is, and we call this vernalization. It's essentially a pretreatment with cold that is necessary for the photoperiod blooming response to take place. Essentially, these plants are still going to be detecting the lengths of those day-night cycles. Right? Examining the relative length of day to night to detect seasonal changes. However, they require a period of cold before that photoperiod response can kick in. And, essentially, this is a way to ensure that they have passed through winter and are going to, for example, bloom in the springtime. And we call this vernalization from the Latin, vernal, for spring.
Now it should be noted that some plants bloom when the plant blooms, but it's thought that it's actually a hormonal signal that causes flowering. Believe it or not, this hormone is yet to be discovered and we simply call the hypothetical hormone, florigen. So essentially, florigen is the hormone yet to be discovered that induces flowering. However, there's good evidence to suggest that such a hormone exists. It can just be trickier than you might realize to actually identify these things when, you know, you don't know exactly what to look for, kind of like searching for a needle in a haystack.