IV. 



mimosa: a typical sensitive plant. 



Uses 



Movement as an adjustment to variations 

 in temperature and light is one of the most 

 necessary and most highly useful adaptations 

 made by leaves. The species that can accom- 

 pHsh the movements most economically will of^ovement 

 have a great advantage in the struggle for 

 existence where the solar factors are most in- 

 tense. In fact it is to be said that no plant in 

 the tropics exposes its leaves to the perpen- 

 dicular rays of the noonday sun. In the 

 species incapable of producing the movement, 

 the adjustment is secured less perfectly by the 

 passive drooping of the leaves. In the tem- 

 perate zone active movements of leaves are 

 exhibited by species of Leguminosae, Oxalidae, 

 Malvaceae, Tiliaceae andMarsiliaceaeonl3^but 

 in the tropics the number is enormously mul- 



* Adapted from a lecture on "Movements of Plants" given 

 betore the Institute of Jamaica, June 19, 1897. 



