Daniel T. MacDougal (1865-1958)

Courtesy Carnegie Institution for Science Administrative Archives

The sweltering Arizona heat settles over a desolate desert. In the distance, Daniel T. MacDougal is hunched over a small white-green cactus. With a large hiking backpack strapped to his sweaty back, he carefully reaches out to the cactus and filters out the minuscule seeds between his coarse fingers. After slowly pouring the seeds into a small tube, he stands up and walks off into the vast desert overflowing with flora. For MacDougal, this is just another ordinary day camping outside and harvesting seeds. He valued being out in the brush as much as he valued his time in the laboratory. Fascinated by a plant’s functional response to arid climates, much of MacDougal’s work involved desert vegetation. Some of his notable works as a desert ecologist were contributing to De Vries’s mutation theory, inventing a dendrograph, and establishing Carnegie’s Desert Laboratory, the predecessor to today’s Plant Biology and Global Ecology departments. 

Daniel T. MacDougal was born in 1865, in Liberty, Indiana. After receiving his Master’s degree at DePauw University, MacDougal earned his Ph.D. from Purdue University. He then completed his post-doctoral studies in Leipzig and Tubingen, Germany. 

In 1890, at an early stage of his career, MacDougal took a great deal of inspiration from botanist Hugo De Vries and De Vries’s Mutation Theory, a theory stating that evolution is a process where mutations generate new species. MacDougal attended nearly all of De Vries’s lectures in the United States. He then helped De Vries compile his lectures into the book Species and Varieties: Their Origin by Mutation. Through this, MacDougal was an essential factor in spreading the word of De Vries’s Mutation Theory. After landing a job at the New York Botanical Garden in 1899, MacDougal began his experiments to prove the Mutation Theory and continued the experiments for several years at Carnegie’s Desert Laboratory. He was a faithful experimentalist and decided that an experimental breeding studies on the evening primroses (Oenothera) would be the best choice for his study. In the end, MacDougal demonstrated that external mutagens induced permanent genetic mutations in gametes by injecting plant ovaries with mutagens. While his claims were not completely true, he was a pioneer in studying the idea of controlling evolution. 

Recognized as a knowledgeable desert ecologist, MacDougal helped establish two significant botanical laboratories. Backed by Carnegie Institution for Science's support, he set up and directed the Desert Laboratory in Tucson, Arizona in 1903 and the Coastal Laboratory (also called Acclimatization Laboratory) in Carmel, California in 1909. At Carnegie, MacDougal made a significant contribution to plant ecology in 1918 with the invention of an auxographic instrument, the MacDougal dendrograph. This measuring device was the first of its kind. It revolutionized the way that researchers could measure tree growth. The dendrograph could measure the growth of a tree year-round. It could also accurately record the fluctuations in tree growth throughout the day and throughout the year. His dendrograph proved to be a valuable instrument for studying tree growth and for those in the forestry industry. 

His time at Carnegie proved fruitful with many publications on the studies of tree growth and their hydrostatic systems. Out of his impactful works is MacDougal’s book, Growth in Trees. Published in 1921, the book encompasses 18 years of various trees he studied on his excursions to Idaho, Arizona, Mexico, and other US states. Utilizing his own dendrograph to make growth measurements, MacDougal soon became the local expert on the Monterey pine and several other deciduous trees. Growth in Trees was one of the first books of its kind to include information about the growth of trees all across North America and became the bed on which America’s knowledge of trees grew. 

In addition to his extensive research on the Mutation Theory with evening primroses at Carnegie, MacDougal spent a great deal of time studying the vegetation at the Salton Sea. The Salton Sea was a basin flooded with water from the Colorado River. Here, MacDougal’s adventurous and curious mind sprung into action. The plants, submerged in the water, greatly intrigued MacDougal and he was committed to studying the plants that were repopulating the base of the Salton Sea. MacDougal then sailed for two weeks with his good friend and researcher Godfrey Sykes in 1905. His time sailing on the gradual shrinking lake is compiled into the book The Salton Sea: A Study of the Geography, the Geology, the Floristics, and the Ecology of the Desert Basin. Just like his excursion to the Salton Sea, MacDougal’s ambitious character provoked trips to the Colorado Delta and the start of other ecological studies. 

The modern fields of desert ecology and plant biology give thanks to MacDougal for his intensive research on desert plants and trees. Through the driven manner in which he approached research and his inclination to study a wide variety of subjects, many look up to MacDougal as a man of great importance in Carnegie’s first steps as a research institution. His research on the Salton Sea, desert plants, and the growth in trees illuminated the possibilities for succeeding ecological research in studying plant adaptations to certain environments.

Photo credit: "Courtesy Arizona Historical Society"