PHYSIOLOGY OF PLANTS 



VOLUME III 

 CHAPTER I 



MOVEMENT 



SECTION I. The Different Forms of Movement. 



No plant is entirely without the power of movement, for even in rooted 

 plants the growing parts move in space, and, since this continues until 

 death, rhizomes and runners may traverse a considerable distance during 

 their existence. 



The tip of a growing organ usually does not follow a straight line, but 

 describes a complicated curve in space. In many cases, indeed, the rates 

 of growth on opposite sides are such that a pronounced curvature may be 

 produced, or the tip may move to and fro, or trace a spiral curve in space 

 as it elongates (circumnutation). These growth or nutation 1 movements 

 naturally cease with the cessation of growth, although active movement 

 may still be possible in some cases. For instance, the pulvini of many 

 Leguminosae, and of other plants also, are organs specially adapted for 

 pronounced movement by elastic shortening and lengthening 2 . The fact 

 that in plastic shoots no movements occur after the cessation of growth 

 simply shows that in these parts the activity of the plant is unable to 

 produce any perceptible effect. If, however, growth is reawakened, as 

 in the nodes of Gramineae by geotropic stimulation, we again encounter 

 curvatures due to nutation. 



In adult but still living parts which are externally rigid, an internal 

 power of movement is never entirely absent, and is indeed permanently 

 connected in every cell with metabolism and exchange, for in the proto- 

 plast itself movements and changes of shape continually occur. 



In the absence of a cell-wall amoeboid movements and changes of 

 shape are possible, as is especially well shown by Myxomycetes. Swarm 



1 This term was first used by Duhamel (Naturg. d. Baume, 1765, Bd. n, p. 115) and de Candolle 

 (Pflanzenphysiol., 1825, Bd. 11, p. 666), and subsequently restricted by Sachs to movements pro- 

 duced by growth (Sachs, Lehrbuch, 1873, 3- Aufl., p. 757), whether autonomic or aitionomic. Frank 

 (Beitrage zur Pflanzenphysiol., 1868, p. 51) uses the term 'nutation' for growth-movements due to 

 external stimuli, and distinguishes autonomic movements as ' inclination.' 



2 Pfeffer, Die Reizbarkeit d. Pflanzen, 1898, p. 9. (Reprint from the Verh. d. Ges. deutscher 

 Naturforscher u. Aerzte, 1893.) 



PFEFFER. Ill 



