The movements of Leaves. 



865 



The leaves of Batihinia grandiflora go to sleep at an unusually early hour in 

 the evening, and in the manner described at p. 373 of "The Movements of Plants," 

 namely, by the two halvcs of the same leaf rising up and Coming into close con- 

 tact : now the leaves of Batihinia Brasiliensis do not sleep, as far as Fritz Müller 

 has seen, but they are very sensitive to a bright light, and when thus exposed 

 the two halves rise up and stand at 45 " or upwards above the horizon. 



Fritz Müller has sent me some cases, in addition to those given in my former 

 letter of March 3 ^), of the leaves of closely-allied plants which assume a vertical 

 Position at night by widely different movements; and these cases are of interest 

 as indicating that sleep-movements have been acquired for a special purpose. 

 We have just seen that of two species of Bauhinia the leaves of one sleep con- 

 spicuously, while those of a second species apparently do not sleep at all, The 

 leaves of Euphorbia jacquinicpflora depend vertically at night, whereas those of 

 a dwarfish Brazilian spezies rise verticalty up at night. The leaves of this 

 Euphorbia stand opposite one another — a position wich is rather rare in the genus ; 

 and the rising movement may be of Service to the plant, as the upper surfaces 

 of the opposite leaves mutually protect one another by Coming into contact. In 

 the genus Sida the leaves of two species rise, while those of a third Brazilian 

 species sink vertically down at night. Two species of Desmodium are common 

 plants near Fritz Müller's house: in one the leaflets move simply downwards at 

 night ; but in the other not only do the three leaflets move vertically down, 

 while the main petiole rises vertically up, as is likewise the case with D. gyrans, 

 but in addition the lateral leaflets rotate so as to stand parallel with the terminal 

 leaflet, behind which they are more or less completely hidden. This, as far as 

 I have seen, is a new kind of nyctitropic movement; but it leads to a result 

 common to several species, namely, that of packing the three leaflets closely 

 together and placing them in a vertical position. 



Down, Beckenham, Kent, April 14. Charles Darwin. 



i) Siehe Ges. Schriften S. 862. Der 3. März ist der Erscheinungstag der „Nature". Der Herausgeber. 



Kritz Müllers gesammelte Schriften. 55 



