122 



Miss M. Wheldale. 



[Apr. 25, 



but only those give a direct action of which the tissues contain more or less 

 organic peroxide. 



The experiments I have made with oxidising enzymes corroborate these 

 doubts. I have found that the power to give the direct guaiacum action in any 

 plant is always accompanied by another phenomenon, i.e. the formation of 

 brown or reddish-brown pigment when the tissues are injured mechanically 

 or are subjected to chloroform vapour. 



Both phenomena are peculiar to certain genera, other genera giving the 

 indirect action only and being unaffected in the same way by injury or by 

 exposure to chloroform vapour. On the whole the direct action is especially 

 characteristic of the Compositae, Umbelliferae, Labiatse and Boraginacese, 

 and certain genera of the Scrophulariacea;, Kosacese, Leguminosee,. 

 Banunculacese, and of many other natural orders. It is absent from or 

 rare in the Cruciferee, Caryophyllacese, Crassulacese, and Ericaceae.* The 

 direct action is also more frequent among the Dicotyledons than the 

 Monocotyledons. 



The results of my observations have led to the conclusion that the direct 

 action given by the extracts of the plants I have examined! is due to the 

 presence of the dihydric phenol, pyrocatechin, in the tissues of the plants. 



That the darkening of plant juices is due to the presence of pyrocatechin 

 has been previously suggested by Grafe.J The same suggestion has also- 

 been made by Weevers§ in connection with his work on the relationship 

 between pyrocatechin and salicin in Salix and Popuhis. 



Pyrocatechin rapidly oxidises on exposure to air, and then acts as an 

 organic peroxide, enabling the peroxidase, which is almost universally present, 

 to transfer oxygen to the guaiacum. The plants, such as I have examined,, 

 from which pyrocatechin is absent do not give the direct action. 



* A similar distribution of direct action has been noted by Passerini, " Sulla presenza 

 di fermenti zimici ossidanti nelle piante fanerogame," 'Nuov. Giorn. Botan. Ital.,' 1899. 

 Also by Clark, "The Plant Oxidases," 'Dissertation,' New York, 1910. 



t The plants examined included Aconitwn Napellus, Caltha palustris, Helleborus 

 fcetidus, Mahonia aquifaltum, Cltciidonium majus, Prunus Laurocerasus, Pyrus japonica,. 

 Cornus mas, Chcerophyllum sylvestre, Ligustrum vulgare, Anchusa officinalis, Myosotis 

 dissitifiora, Rosmarinus officinalis, Viburnum Opulus, V. Tinus, Sambucus nigra, and 

 Taraxacum officinale, in all of -which pyrocatechin is present. Pyrocatechin was not 

 detected in Crocus vermis, Galanthus nivalis, Arabis albida, Eranthis hyemalis, 

 Cheiranthus Cheiri, Brassica oleracea, Viola odorata, Primula acaulis, Iris germanica, 

 Lupinus sp., Narcissus Pseudo-narcissus, nor in Arum maculatum. 



X Grafe, " Uber die Dunkelfarbung von Eiibensaften,' ' Oest. Zeitsch. f. Zuckerindus. 

 u. Landwirtschaft,' 1908. 



§ Weevers, " Die physiologische Bedeutung einiger Glykoside." Extrait du ' Recueil 

 des Travaux Botaniques Neerlandais,' vol. 7, 1910. 



