Marie Clark Taylor

Exposing plants to different day lengths changes their flower development

Contributed by: Riley Pizza @RileyPizza




Agriculture, Black, Development, Experimental, Flowering, Fundamental research, Historical figure, North America, Physiological/organismal ecology, Plants, Race/ethnicity, Terrestrial, Woman



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Clark, Marie B. The Influence of Definite Photoperiods upon the Growth and Development of Initiated Floral Primoridia, Fordham University, Ann Arbor, 1941. ProQuest link



Slide 1: Researcher’s Background

Marie was a plant physiologist researching plant growth in response to light, in addition to her passion for increasing the use of botanicals in elementary education.

Biography in brief

Marie was the first woman of any race to graduate with a PhD from Fordham University in 1941. In 1945 she became a professor at Howard University’s department of Botany, and was the head of the department from 1947-1976. Outside of her research, she is best known for her impact on high school teaching. Marie was a huge proponent of using plants in classrooms since they were affordable and widely available, compared to animal specimens. She organized a series of instructional workshops for high school teachers to learn about using plant materials to teach their students. Under the NSF, Marie helped put together 16mm instructional films that teachers could use, ranging from plant growth time-lapse videos to biographies on researchers such as Louie Pasteur. Her methods were so impressive that in the mid 1960’s she was specifically requested by president Lyndon B Johnson to bring her work nationally and internationally! After her death in 1990, her former colleague and civil rights activist Margaret Strickland Collins said Marie was “a powerhouse who worked tirelessly to improve teacher training in the sciences” 

Is (or was) their research under-valued because of their identity?


Slide 2: Research Overview

Take home message of study

The development of scarlet sage flowers was altered when exposed to short day lengths (6hrs of daylight) or long days (16hrs or daylight). Under short days, flower production was slower than normal, and under long days flowers were not produced at all. 

Study system

This is a photo of a Scarlet sage raceme, taken from wikicommons. Note that the raceme is the entire stalk, containing many flowers. 


Slide 3: Key Research Points

Main figure

This graph shows the percent of plants in each light treatment group (y axis) and the length in mm the racemes (a long stalk containing many flowers) grew during the experiment (x axis).  A good way to think about racemes is that the longer they are, the more flowers are on them, and thus greater reproduction for the plant.  For simplicity, I would focus on the peaks for each of the lines. What this graph is showing is that most of the plants grown under low day lengths (6hrs) produced racemes that were half as long as those under medium day lengths(10hrs). Those grown under long day lengths (16hrs) tended to have the shortest racemes, although there were a few that were taller/as tall as the 6hr plants. 

As a note, Marie couldn’t get plants under the 16hr day lengths to flower unless they were first exposed to 10hrs of light and, once flowering started, were put into the 16hr treatment. 

A fun fact:  While scientists now can have computers make their graphs, Marie didn’t have Microsoft excel and had to draw all her graphs by hand!  If you look closely, you can see the pencil marks she made at each point!


Societal Relevance

Understanding how plants respond to light, especially when it comes to flower production, is really important for anyone trying to optimize the number of flowers and/or fruits a plant produces. Think, if you were the owner of a flower shop and wanted the most beautiful scarlet sage, what day length would you grow them at?

If people are trying to get crops like soybeans to produce the most beans, they need to know when the best time to plant them is, so when the plants are ready to flower and produce beans the day lengths are optimized so the most number of beans can be collected. 

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