Biological Papers. 97 



THE EFFECT OF LIGHT ON MELILOTUS ALBA. 



(Sweet Clover.) 



By R. W. CoppEDGE, Mulvane. 



npHE MeliloUis alba, or Sweet clover, was taken up as an inter. 

 ^ esting plant to study because it seemed able, to a remarkable 

 degree, to adapt itself to its surroundings. It is one of the earliest 

 plants to appear in the spring, coming up, especially on a south or 

 southeast slope, two or three weeks before any other plant. By the 

 last of March the leaves begin to appear, and on every bright, sunny 

 day the work of forming starch is going on in its laboratories. 



By means of its tubercles it is able to extract nitrogen from the 

 atmosphere. We find it, therefore, in great abundance in blue shale 

 and clay soil, where few, if any, other plants can grow. 



The readiness with which the leaves and growing stem respond 

 to the light enables the plant to protect itself from heat and cold, 

 and keep its leaves in the best position for forming starch. 



Experiments have been made by the author during the months 

 of April and May of 1899 and 1900 to find out, if possible, just how 

 rapid these processes were. 



First, as to the nutation of leaves and stems : Kellerman, in his 

 paper read before the Kansas Academy of Science, proved that the 

 Helianthus annuus did not nutate, thus disproving popular tra- 

 dition. He had only worked on plants, however, after anthesis. 



Schaffner proved, by a number of experiments conducted in 

 1896-'97, that prior to anthesis the leaves and flower-heads nutate 

 during the day in such a way as to stand at right angles to the sun's 

 rays. Ki night the leaves drop, with points turned toward the 

 ground, occupying a sleep position.* 



W. P. Wilson and Jesse M. Greenman conducted a number of 

 experiments along the same line on the MelUotus alba. Their ex- 

 periments were to show the regular daily movements of the plant. 

 They found four positions which the leaves take, three normal and 

 one abnormal. The first or normal day position may be seen in 

 the morning or evening. The leaves are spread out, with the 

 blades at right angles to the sun's rays. 



In the second or hot-sun position the leaves stand with their 

 tips pointed toward the sun, the blade parallel to the sun's rays. 



* Observations on the Nutation of Helianthus annuus, Bot. Gaz., vol. 25, pp. 395-404. 



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