6a4 



LECTURE XXXVI. 



But the foliage-leaves of very many other plants also, in which no special 

 motile organs are observable, make daily movements resulting in the production of 

 diurnal and nocturnal positions : the growing petioles undergo curvatures by which 



FIG, ^^.—Dtsmodium gyrans. A shoot during the day; B shoot with leaves asleep. 

 From reduced pllotographs {Darwin). 



the laminse situated on them are presented to the light during the day, and at night 

 are directed upwards or downwards. 



mention only a few more recent works which will at once place the beginner on the right path in 

 this province. 



Sachs, ' tJber das Bewegungsorgan und die periodiscke Bewegungen der Blatter von Phasiolus 

 und Oxalis,'"Bot. Zeit. 1857 (p. 793). 



Sachs, 'Die voriibergehenden Starreztistdnde periodisch beweglicher und reizbarer Pflaneen- 

 organs' Flora, 1863 (Nos. 29, &c.). 



Paul Bert, ' Mimoir. d. I. soc, d. scienc. phys. et naturell, d. Bordeaux' (1866). 



Millardet, ' Nouv. recherches sur la piriodiciti d. I. tension^ 1869 (Mem. de la soc.natur.de 

 Strasbourg). 



Batalin, ' Ober die Ursachen der periodischen Bewegungen der Blumen und Laubblatter! Flora, 



1873 (P- 433)- 



Pfeffer, ' Physiologische Untersuchungen^ Leipzig (1873 and 1875). 



Sachs, ' Lehrbuch der Botanik,' IV Aufl., 1874 (pp. 844-869). 



I cannot agree with the nomenclature introduced into this subject by Pfeffer. His ' Reception!' 

 bewegungen ' are simply ' Reiz-bewegungen! the peculiarity of which, that they take place only while 

 the organ is in a condition of phototonus, I characterised in 1865 by the expression ' paratonic stimu- 

 lation,' an expression moreover which Pfeffer accepts, though it makes the term 'Receptions-bewegung, 

 which in fact can only hold for this case, superfluous. Again, I can by no means agree with Pfeffer'S 

 designation of the periodic movements of non-articulated foliage-leaves as movements of nutation, 

 although he himself as well as Batalin demonstrated their dependence on variations of light; 

 for the term ' nutations,' previously introduced by me, applies simply to inequalities of growth on 

 different sides of an organ, which are not induced by external influences. It would be much to 

 be deplored if in this difiicult province, where Nature herself presents plenty of confusion, still 

 further difficulties should be produced by an indefinite nomenclature. 



