16 



retain the necessary minimum of water. But tlirough various influ- 

 enc^s, such as exposure of the tissues to a salt solution whose concen- 

 tration exceeds a certain limit, this power of adjustment may be 

 temporarily lost. In such cases a considerable proportion of the cell 

 water diosmoses through the ectoplasm, and the protoplast in conse- 

 quence shrinks away from the cell walls, to which it is normally 

 closely applied. If the unfavorable condition persists, this tem- 

 porary plasmolysis may become permanent, and the cell is killed 

 outright. 



Such disorganization due to extreme plasmolysis can usually be 

 detected immediately by an examination of the plant tissues with the 

 microscope, and is one of the best indications of death. ^ Roughly, 

 however, injurj^ of this nature is sufficiently indicated after a certain 

 lapse of time by loss of rigidity and elasticity in the plant or part of 

 a plant affected; in other words, it becomes flaccid. If, for example, 

 a root thus rendered flaccid by culture in a salt solution fails to regain 

 its turgor after being transferred to water or to a nutritive solution, 

 it ma}' safely be considered as injured beyond recovery. This was 

 found to be the m6st satisf<ictory test of death employed. ^ 



The color of the tissues is often a useful symptom of destructive 

 changes. Thus all the sodium salts employed, when given in suffi- 



^ "The only externally perceptible change [indicating death] is in many cases 

 collapse, a more or less strong, irregular recession of the protoplast from the cell 

 wall, which does not, however, accompany by any means all reactions of sub- 

 stances which occasion death." [Klemm, Desorganisations-erscheinungen der 

 Zelle. Jahrb. fiir wiss. Botanik, 28, p. 657 (1895).] 



•^ Sachs [Arb. bot. Inst. Wiirzburg, 1, 386; Gesammelte Abhandl., 2, 774] men- 

 tions as an indication of the approaching death of the root tip the disorganiza- 

 tion of the cells of the root cap, which becomes mucilaginous. This was noted in 

 many cases, but was not found to be a practical test of complete loss of vitality. 

 Another indication of injury to the apical portion of the root is a sharp bend 

 near the tip, which is very different from the normal gentle curvatures. This 

 usually appears where loss of turgor from plasmolysis is not manifested. While 

 indicating injury, this symptom by no means necessarily implies complete loss of 

 vitality and, therefore, does not serve our purpose as a symptom of death. Solu- 

 tions of a certain concentration of magnesium sulphate, magnesium chloride, and 

 calcium bicarbonate were found to produce this phenomenon in a marked degree. 

 In the case of the salt last mentioned the roots continued to grow slowly in dis- 

 tilled water, during a second period of twenty-four hours. True [Ann. of 

 Botany, 9, 377, (1895)] alludes to these " sharp curves characteristic of injury." 



Another means of detecting loss of vitality in protoplasm, to which, however, 

 recourse was not had in the progress of this work, is its coloration when dead by 

 means of nigrosin, v/hich does not color and does not injure living protoplasm. 

 See Pfeffer [Ueber Aufnahme von Anilinfarben in lebende Zellen. Unters. aus d. 

 bot. Inst. Tiibingen, 2, 268, 269], who found in experiments with roots of duck- 

 weed (Lemna) and with Spirogyra that nigrosin is not absorbed by cells while 

 alive. Living root hairs exposed for three days to a 0.5 per cent solution of this 

 stain assumed no coloration whatever, while hairs after death when similarly 

 treated readily absorbed it. 



