34 RELATIONS OF PLANTS TO MECHANICAL FORCES 



sists in increased respiration, as indicated by an increase in the 

 amount of carbon dioxide exhaled, and the rise in temperature. 

 Later reactions of a regulatory nature consist in the degeneration 

 of the injured protoplasts, the renewed growth of neighboring 

 resting cells, and some instances may be followed by the forma- 

 tion of a new tissue which has for its purpose the closure of the 

 injured surface of the organism. An example of this is to be 



FIG. 17. Diagrams showing proper location of incision stimuli. 



found in the callus formations of cuttings and trees. A few organs 

 such as roots and tendrils are capable of manifesting special move- 

 ments in response to injury which may have for their purpose the 

 withdrawal from the source of the injury. It is to be noted in 

 this connection that the destruction of a tissue will often be fol- 

 lowed by purely mechanical curvatures, resultant from the release 

 of a stress set up by the tissue when in its place. l 



49. Traumatropic Curvatures of Roots. Prepare a number of 

 seedlings as in 42. After the seedlings have been fastened to 

 the cork cut the thinnest possible slice from one side of the tip, 

 being careful not to remove more than one-fourth of the apical 

 region, and not .amputating the extreme tip (Fig. 1 7). Put the 

 cork in place with the roots in a perpendicular position and note 

 results a day and two days later. The seedlings may also be 

 grown in moist sawdust in which they are placed in the same rela- 

 tive position after being treated as above. 



50. Changes in Roots Stimulated Traumatropically. Nemec 

 finds as a result of thorough investigations that the cells in the 

 neighborhood of the injured surfaces of roots undergo various 

 changes inclusive of a very marked vacuolization which it is be- 



1 Nemec, B. Die Fortpflanzung des Wundreizes. Die Reizleitung und Reizleiten- 

 den Strukturen bie den Pflanzen, 16. 1901. 



