F. Keeble and E. F. Armstrong 281 



As the result of an extended trial of the many reagents which have 

 been employed for the purpose of demonstrating oxydase we find that 

 the most serviceable for our purpose are a-naphthol and benzidine. We 

 make use of the fact demonstrated by one of us (Armstrong, 1910) that 

 substances dissolved in alcohol penetrate rapidly into plant cells, and 

 the method which we employ is as follows : 



In the case of benzidine, a 1 per cent, solution is made in 50 per 

 cent, alcohol which is then diluted with so much water as not to cause 

 a precipitate. The object to be examined, for example, an intact 

 corolla or a section of a petal of P. sinensis, is taken from the plant 

 and placed immediately in the reagent in a corked specimen tube. 

 The tube is incubated at 37° C, and if no direct oxydase reaction is 

 obtained the material is removed from the tube, washed lightly with 

 water and treated with 1 to 2 drops of 10 vols, hydrogen peroxide, or 

 the latter reagent may be added directly to the tube containing 

 benzidine. In the case of o-naphthol, the solution may be used of 

 even less alcoholic strength. Sections may be prepared either with 

 a dry razor or with one moistened with a solution of cane sugar of 

 suitable strength. No inhibitory action appears to be produced by 

 this substance. The first effect of treating coloured flowers with either 

 of these reagents is a decolourisation of the pigmented parts. This 

 decolourisation appears to be due to the action of a catalase, but we have 

 not made it a subject of special investigation. 



As we show in detail in Section II. the result of treating a coloured 

 or recessive white flower of Primula sinensis is the demonstration of 

 peroxydase in the epidermal layer of the petals and also in the bundle 

 sheath which surrounds and accompanies the veins in their finest 

 ramifications. 



Preparations of a considerable degree of permanence may be made 

 for demonstration purposes in the following manner: — The flower in 

 which the oxydase reaction has developed is washed well in running 

 water, the corolla tube is cut away, the petals floated on water, whence 

 they are transferred by means of filter paper to a glass lantern slide. 

 The superfluous water is removed by means of filter paper, and dry 

 filter papers are placed over the flattened flower, A glass slide is 

 laid on the filter paper, the preparation is placed in the incubator at 

 37° C. and pressed down by means of a weight. After a day or two, 

 when the preparation has become dry, it is treated as a lantern slide, 

 bound and kept in a dark place. The degree of permanence seems to 

 depend first, on the thoroughness with which the preparations are washed. 



