TRAUMATIC EFFECTS 133 



SECTION 38. Traumatic Effects. 



Severe injuries produce reactions which not only affect the part 

 injured, but often more distant ones also. Probably^the smallest injury 

 is not without effect, though no visible response may ensue. The reaction 

 is mainly directed towards the repairment of the injury, and the whole of 

 the phenomena involved in the traumatic response may be grouped under 

 the term wound-reaction. In simple cases the wound-reaction involves 

 little more than the replacement of a missing part, such as the two new 

 pieces of the peripheral membrane formed when a plasmodium is cut in 

 two, or the transverse walls formed at the opened ends of filaments of 

 Vaucheria. When multicellular hairs or filaments of Spirogyra are cut 

 through, the exposed transverse walls assume the same peculiarities as the 

 original external walls. 



In tissues the injured cells usually die, and the reaction takes place in 

 the neighbouring living cells, and may spread to others more remote. Fre- 

 quently the reaction merely consists in the cuticularization or other changes of 

 the exposed cell-walls, but often a cork-layer may be formed over the exposed 

 surface, either from a new cork-cambium, or by the gradual modification 

 of the callus-tissue formed at first. The growth of the callus-tissue often 

 leads to the filling up of wounds, or the replacement of the missing parts, 

 and roots and buds may even be produced from it 1 . At the same time, the 

 renewed activity of growth is accompanied and frequently preceded by an 

 increase in the respiratory activity, and in the production of heat. The 

 latter, and other responses also, may even occur in tissues of such character 

 that no growth is possible, or in which it is mechanically prevented. Among 

 such reactions are alterations in the rate of protoplasmic streaming or its 

 appearance, changes in the mode of cell-division, and modifications of the 

 normal metabolism leading to the production of gum over wounds. 



The increased respiratory activity and the appearance of streaming 

 may spread to some distance, even when the growth-changes are restricted 

 to the immediate neighbourhood of the injury. When, however, entire 

 organs are removed, or conducting channels broken, the ensuing general 

 disturbance may lead to growth-reactions in the most widely distant organs. 

 Thus, the removal of the assimilating leaves naturally unfavourably affects 

 the growth of the roots, while the plant strives to replace missing organs 

 wherever this may be possible, whether near to the injury or far away from 

 it. The results due to the mere absence of an organ and other secondary 



1 Cf. Frank, Krankheiten d. Pflanzen, 2. Aufl., 1892, Bd. I, p. 31 ; Sorauer, Pflanzenkrankheiten, 

 1886, 2. Aufl., Bd. I, p. 533; Rechinger, Verh. d. Zool.-Bot. Ges., 1893, p. 310; Maule, Bibl. hot., 

 1895, Heft 33; Peters, Zur Kenntniss d. Wundholzbildung, 1897 ; Massart, La cicatrisation chez les 

 ve"ge"taux, 1898; Kiister, Flora, 1899, p. 142. 



