232 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



ture of the latter, which would be changed by cyan- 

 hydrin formation. But this leaves the action of carbonic 

 acid quite unexplained. Also on one occasion it was 

 found that such an inhibitor appeared to have been partly 

 removed by keeping Iris flowers in water saturated with 

 toluene for about a day. Since toluene, hydrogen cyanide, 

 and carbon dioxide, all render protoplasm permeable 

 without precipitating colloids, as does treatment with 

 alcohol, it is likely that such apparent destruction of 

 inhibitor is really due to its elimination by diffusion. 

 Further experiments on this point are desirable. It may 

 be added that the artificial ripening of persimmons sub- 

 jected to high pressures of carbon dioxide has recently 

 been studied by Lloyd (1911), and may be cited as an 

 example of the effect of this gas in rendering the proto- 

 plasm more permeable, so that enzymes and their sub- 

 strates can come into contact readily. [See note, p. 302.] 



SECTION IL DISTRIBUTION OF OXIDASES IN PLANT 

 FAMILIES. 



PLANTS WITH COMPLETE AND INCOMPLETE PEROXIDASE 

 SYSTEMS. 



There is considerable evidence for the belief that oxi- 

 dases are present in every vegetable cell, though their 

 amount and degree of activity varies greatly. 



Their detection may be effected in many cases by simply 

 bruising or cutting the tissue, which is then seen to darken, 

 owing to the action of the enzyme upon a naturally occur- 

 ring chromogen. The correctness of this explanation is 

 shown by the failure of boiled tissues to darken, and by the 

 fact that, in those which darken naturally, oxidation of 

 added artificial chromogens is also brought about. The 

 darkening of the sap pressed from some plants is very 



