WILLIAM J. ROBBINS 



The New York Botanical Garden 



The Expanding Concepts of Plant 



Growth Regulation 



The Origin of Species by Means of Natural Selection or the Preserva- 

 tion of Favoured Races in the Struggle for Life, written by Charles 

 Darwin, was published in 1859 — one hundred years ago. The cen- 

 tennial observances attest to the stature Darwin has attained. 



Charles Darwin was a botanist and, had he never written the Ori- 

 gin of Species, would be remembered today as one of the major bo- 

 tanical scientists of the nineteenth century. In fact, Charles Darwin's 

 investigations of the sensitiveness of plants to light and gravity may 

 justly be considered, in many ways, to have laid the foundations for 

 our knowledge of plant growth regulators. 



His observations and conclusions were published in 1880 in a 

 book entitled The Power of Movement in Plants (4). Chapter IX 

 deals with the Sensitiveness of Plants to Light: Its Transmitted Effect. 

 Chapter XI deals with Localized Sensitiveness to Gravitation and Its 

 Transmitted Effect. 



In a series of ingenious experiments Darwin explored the responses 

 to light of the coleoptiles of seedlings of Phalaris canariensis and 

 Avena sativa, which had been decapitated or had been covered with 

 caps of tinfoil; gold beater's skin, either transparent or painted so 

 as to be impermeable to light; pipes of very thin glass or quills — 

 some blackened; bandages of tinfoil applied to various parts of the 

 coleoptile; coats of India ink and other procedures. The results of 

 his experiments led irresistibly to the conclusion that the stimulus 

 of light was perceived by the tip of the coleoptile and transmitted 

 to the base where movement occurred. 



Darwin says, 'Trom these several sets of experiments, including 

 those with the glass tubes, and those where the tips were cut off, we 

 may infer that the exclusion of light from the upper part of the coty- 



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