THE DETAILED ACTION OF POISONS 265 



quite possible. High temperatures do in fact cause a cessation of growth 

 and movement in spite of the increased activity of respiration. It is 

 evident that we have in this differential action an important aid to research, 

 and in fact ether, chloroform, and other substances are often used for 

 such purposes. 



Poisons may also influence the mode of growth and hence the 

 resultant shape of the plant. Any such change is at once an evidence 

 of an alteration in the activity of the protoplast, which in etherized plants 

 of Spirogyra is shown by the replacement of mitotic by amitotic nuclear 

 division. In addition various reversible deformatory changes may be 

 induced in the protoplasm by the action of poisons. 



In their responses to poisons plants resemble the lower animals, while 

 in Vertebrata, owing to the complexity of organization, reactions such as 

 the changes in the beat of the heart or in the respiratory mechanism occur, 

 which are absent from the lower organisms. 



The visible effects produced in the plant and in the protoplast by a 

 poison are the result of the primary reactions between the protoplasm 

 and the poison, but we are profoundly ignorant as to the precise nature 

 of these primary reactions. Nevertheless the behaviour of the protoplasm to 

 different chemical substances may afford important indications as to its struc- 

 ture, composition, and properties. It is the nature of the protoplasm which 

 determines whether a substance shall act as a poison or not, and we can 

 therefore mainly restrict ourselves to the individual cell. In vascular plants 

 problems of translocation and of correlation also come into play, for a 

 poison can naturally exercise no influence upon a particular internal cell 

 if it is absorbed and retained by the intervening tissues, while the action 

 of a poison upon one organ may result in related organs being also affected. 

 Even in an isolated cell the poison must first pass through the cell-wall. 

 Hence the presence of a relatively impermeable cuticle may render a 

 cell capable of withstanding immersal in a highly poisonous solution, 

 owing to the fact that fewer molecules of the poison bombard the 

 protoplast in a unit of time than when a cell with permeable walls is 

 immersed in a solution of nearly non-poisonous dilution. Cuticularized hair- 

 cells behave in this way, and it can easily be seen that poisonous aniline 

 dyes or ammonia only penetrate their protoplasts very slowly 1 . 



A poisonous action can only be exercised when the poison penetrates 

 the protoplasm. In this case methyl blue acts as a poison in extreme 

 dilution (i : 1,000,000), whereas as much as I per cent, can be accumulated 

 in the form of non-diosmosing compounds in the cell-sap without the cell 

 being injured 2 . Similarly the non-diosmosing tannate of methyl blue is 



1 Pfeffer, Unters. a. d. Bot. Inst. zu Tubingen, 1886, Bd. II, p. 201 seq. 



2 Id., 1. c., p. 184. Methyl violet behaves similarly, its diosmosing salts being even more 

 poisonous than those of methyl blue. Overton (Vierteljahrsschrift d. Naturf. Ges. zu Zurich, 



