624 



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, :ß^.—Des»wdi 



ryrans. A slioot during the day ; B shoot 

 From reduced photographs (Darwin). 



the laminae 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, ' Über das Bczuegitngsorgan und die periodische Bewegungen der Blätter von Phaseolus 

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



Sachs, 'Die vorübergehenden Starrezustände periodisch beweglicher jind reizbarer Pßanzen- 

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



Paul Bert, 'Memoir, d. l. soc, d. scienc. phys. et naturell, d. Bordeaux' (1866). 



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

 Strasbourg). 



Batalin, ' Über die Ursachen der periodischen Bezuegungen der Blumen und Laubblätter ^ Flora, 



1873 (P- 433)- 



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



Sachs, 'Lehrbuch der Botanik,' IV Aufl., 1874 (pp. S44-869). 



I cannot agree with the nomenclature introduced into this subject by Pfeffer. His ' Peccptions- 

 bewcgmigen ' are simply ' Peiz-bewsgungen,' the peculiarity of which, that they take place only while 

 the organ is in a condition of phototonus, I characterised in 1S65 by the expression ' pai-atonic stimu- 

 lation,' an expression moreover which Pfefter accepts, though it makes the term ' Peceptions-bezvegung' 

 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 difficult province, where Nature herself presents plenty of confusion, still 

 further difficulties should be produced by an indefinite nomenclature. 



