366 PLANT PHYSIOLOGY 



the flowers close, which indicates that this growth movement is 

 reversible and due to changes in turgor. 



Turgor changes produced by shock with consequent movement 

 have been discussed in the case of Mimosa. Similar movements 

 resulting from the loss of turgor are to be seen in the barberry 

 (Berberis), the stamens of which fly upward and inward close to 

 the stigma if touched at the base during the pollen-bearing season. 

 In some of the Cynareae (Composite), the filaments contract when 

 touched, and, as they slide down over the style, the pollen is 

 scraped out. In still other plants (Tecoma starts, Diplacus glu- 

 tinosus, and Crescentia cujete) the stigmas are sensitive and close 

 when touched, as described by Newcombe (1924). Another ex- 

 ample of note is Venus's flytrap (Dionxa) which bears trigger hairs 

 on the leaves. If these are touched by an insect, the two halves of 

 the leaf lock together quickly thus capturing the insect. Here the 

 change in turgor occurs in the midrib of the leaf, where the os- 

 motic pressure increases when the leaf closes. This growth is 

 permanent and the leaf remains closed until the cells on the upper 

 side grow and open the leaf again (Brown, 1916). In Drosera, on 

 the other hand, during bending the cells on the concave side of the 

 tentacles decrease in osmotic pressure, while those on the convex 

 side remain the same (Hooker). These shock movements are some- 

 times called seismonastic. 



It is often hard to separate autonomic from paratonic move- 

 ments. In the case of Desmodium, it has been mentioned that the 

 rate is affected by temperature. To that extent, the movement is 

 paratonic even though the initial cause is unknown. The term 

 "autonomic" is merely a word to cover our ignorance. Similarly 

 it is hard to distinguish growth movements from turgor move- 

 ments for reasons which are obvious to the careful reader. Never- 

 theless, for purposes of classification, the attempt to distinguish 

 between these various types of movements has been made. The 

 student must always remember, however, that all classifications 

 are man-made, as helps to the memory and nothing more. 



Growth Movements. — The movements due to permanent 

 growth are curvatures which are produced by unequal growth. 

 One side grows more than the other with the result that bending 

 takes place. As in the case of the turgor movements, some cases 

 are found in which the causes are as yet unknown ; the regulating 

 factors are internal and therefore difficult to determine exactly. 



