Up until the last few days of December 2015, the Northeastern U.S. was experiencing record breaking high temperatures. Holiday enthusiasts lamented the heat and the inevitable lack of a white Christmas, ice fishermen in northern Maine looked sullenly out at the open water, and confused daffodils began poking up through the dirt.
Temperature Records in December 2015
When winter finally arrived in Princeton, NJ, the temperature plummeted to below freezing and all of the freshmen from California learned that they would in fact not be able to survive the entire year with just a sweatshirt. A chorus of whining erupted on social media from all of the students who were now forced to scurry between buildings under layers of down and wool. (The true moral of the story is that people will really never be happy about the weather unless they’re spending time in the tropics and it’s not hurricane season.)
This post, however, will focus on the quieter victims of this erratic weather. Specifically, it will investigate the impact of these temperatures on flowers of the Forsythia viridissima bush that grows outside the McCosh Health Center on the campus of Princeton University. (Please note that I’m not a plant specialist, but my research indicates that this is the species of the plant I studied) This type of Forsythia typically blooms between March and April, and the fact that it was in full bloom in early January indicates that the plant was likely deceived by the balmy December weather. Hopefully, this investigation will provide a larger commentary on the plants that were tricked into blooming early through the literal lens of the exposed petals of Forsythia viridissima. After having watched my daffodils thwarted by the frost many times throughout my life, I look forward to investigating the impact of the cold on the delicate petals of a flower.
I collected several samples from branches around the forsythia bush, trying to get samples from the outside of the bush as well as some that were sheltered within the dense branches. This collection occurred on January 5th, just about a week after the radical temperature change.

One of the selected branches

Dense branches of the forsythia

Individual buds
I then plucked off the buds, separating them by whether or not they had already bloomed. My hypothesis was that the flowers with exposed petals were more susceptible to the change in the weather and the below freezing temperatures and therefore would therefore be more damaged than the internal petals of the unopened buds. Specifically, I was interested in the appearance of the different petals’ cells and their pigmentation. I carefully cut off petals from the flowers and created two sample slides: the first featured three larger petals from three different exposed blooms and the second had four smaller petals from four different unopened buds.
This is what I found.








Closeup on the exposed petal
Exposed Petals
The exposed petals, pictured above, had very clearly delineated cells, with dark cell walls and lighter interiors. The color was slightly browner than that of the protected petals, despite the fact that both sets of photographs were taken at the same time, using the same camera and the same light source. Individual veins are clearly visible.










Closeup on a protected petal
Protected Petals
I had significantly more difficulty getting a focused picture of the protected petals which had been on the inside of the closed bud. This might have been because the camera itself was having trouble focusing or because there was a heavier covering of a pollen-like substance on the petal itself which made it more difficult to focus on individual cells. The individual veins were significantly less apparent and the petals were all a brighter shade of yellow.

This investigation yielded some pretty interesting results, although none of it is entirely conclusive, and what follows is conjecture based on my basic knowledge of plant cell structure.
The fact that individual cells were significantly more apparent on the exposed petals suggests that the vacuoles in the cells had dried out, leaving the cell walls as the surviving structural component of the petals. This, along with the fact that the veins were more evident, indicated to me that the cells of exposed petals were significantly less robust than their sheltered counterparts, with only the major structural components remaining strong. In comparison with the sheltered petals, the exposed samples were clearly thinner and more transparent, indicating that the harsh weather conditions indeed had negative effects on the exposed petals.
Future research into this area could take into account different species of flowers. It would also be helpful to take samples over a period of time and investigate the consequences of a particularly warm or cold week on the blooms of the forsythia. It would have been helpful to have taken a sample bloom before the first frost, but I lacked the foresight to photograph one of these blooms, so future research could take a sample before and after the first frost. With increased knowledge of the effects of cold, members of the microcosmos might even be able to develop and test methods of protecting these vulnerable early flowers.
While the mistaken preemptive bloom is likely not helping the forsythia plant, there are other who can benefit from its early flowers. Now, as students walk past in shivering huddles, they can can admire the tangle of bright yellow, cheerful and resilient despite the chill.

I conducted this project as part of Professor Pringle’s EEB321 class at Princeton University.