364 PLANT PHYSIOLOGY 



rangium closes and the cells resume their former position. The 

 walls of anthers and the sporangia of other Pteridophytes be- 

 have in a similar manner, usually without sudden move- 

 ments. 



Turgor Movements. — Turgor movements are due to changes 

 in the water content of the cells without any increase in number 

 of cells and unaccompanied by any other growth changes. Such 

 movements are produced (1) by external causes which can be 

 modified at the pleasure of the investigator, or (2) by internal 

 conditions of unknown cause. The former are called paratonic 

 and the latter autonomic. 



Autonomic movements due to turgor pressure are comparatively 

 rare and are confined almost entirely to leaves or their modifica- 

 tions. In the Leguminosa?, Oxalidaceae, and a few other families, 

 the leaf base is swollen to form a parenchymatous pulvinus as 

 described for Mimosa (Chap. XXVIII). Variations in the turgor 

 on various sides of this pulvinus cause the leaf to describe a circle 

 or ellipse. While this movement is not rapid and requires special 

 apparatus for its observation in the majority of cases, in the 

 classic case of Desmodium gyrans the movement can be seen with 

 the unaided eye. Here the tips of the leaflets move in an elongated 

 ellipse with a path several millimeters long. The movement is 

 sometimes uniform but more often intermittent or jerky, from 

 which the common name of " telegraph plant" has been derived. 

 Under room temperatures the entire traject is covered in 3-5 min- 

 utes, but at higher temperatures the speed is increased so that 

 the entire course may be completed in a half minute. Similar 

 movements are displayed by the leaves of Eleiotis bahave. The 

 advantage of such movements to the plant is unknown. 



In addition to these rotating movements or nutations, leaflets 

 undergo in some cases an up and clown motion in one plane. In 

 the common red clover (Trifolium), the leaflets slowly rise and 

 fall, completing an entire traject in one to four hours. This move- 

 ment in one plane, produced by changes in turgor of the two sides 

 at the base of a dorsiventral organ such as a leaf or petal, is 

 known as a nastic curvature. In nutations, the organ moves in 

 more than one plane, while in nastic curvatures the movement is 

 in only one plane, owing to the fact that the structure of the organ 

 prohibits movements in other directions. 



Of the paratonic nastic movements due to changes in turgor, 



