KEEPING WARM 
Flowers That Make Heat 
While the Sun Shines 
Some plants that bloom at low temperatures act as solar collectors, 
hastening the growth of pollen and seeds 
by Roger M. Knutson 
My first thought at the sight of a bee. 
fly. beetle, or mosquito scrambling 
across a sunlit, early spring bloom is that 
food needs are being met. Therefore, 
when one of my students on a botany 
field trip a number of years ago asked 
me why so many of the early spring 
flowers in the forests of northeast Iowa 
were white, I responded that they were 
easier for potential pollinators to locate. 
While that may or may not be true, their 
brilliance certainly makes it easier for 
people to see them in the low-angled sun 
that strikes the forest floor before the 
trees leaf out. The student’s question, 
however, returned to mind in subse- 
quent springs, and as I thought about it, 
other generalizations about early spring 
bloomers suggested themselves. Many 
of the flowers are bowl or saucer shaped; 
they are often more or less heliotropic, 
or sun following; they tend to have re- 
flective petals; and they frequently have 
centers composed of many fuzzy sta- 
mens and carpels. I conjectured that 
many of these flowers might be accumu- 
lating heat by behaving like small dish 
antennas, focusing reflected light and 
heat on the flower center where reradia- 
tion among the stamens and carpels 
would effectively retain the heat for a 
time. 
That the green leaves of plants use 
sunlight for photosynthesis has been 
known since the late eighteenth century, 
but how flowers might use solar energy 
for heating is less well understood, possi- 
bly because we cannot see the energy 
that flowers capture. The red and blue 
colors visible on the edges of every rain- 
bow are essential to the all-important 
food-making processes in plants, but be- 
yond the blue and red are colors — wave- 
lengths of electromagnetic radiation — 
Pasqueflowers Brara**:^ 
75 
