Atkins — Oxydases and their Inhibitors in Plant Tissues. 149 



leaf as a whole fails to give any oxydase reaction, with the exception of that 

 from the extreme tip which affords the indirect reaction with guaiacum. This 

 irregular distribution leads one to suspect the presence of some reducing 

 agent, which prevents the detection of the oxydase. 



The purple flowers yield an intensely coloured sap when pressed. The 

 brown markings at the bases of the perianth leaves are due to the optical 

 combination of yellow plastids with a purple cell-sap. The purple pigment turns 

 red with an acid, and this red is stable. With alkalis, however, a green 

 fading to pale straw is produced. Neutralization does not restore the purple, 

 nor does acid now turn the sap red. Thus alkalis quickly destroy the pigment. 

 A very faint trace of ammonia vapour alters the purple to a beautiful shade 

 of blue, but this fades through green to straw in a day. This coloured extract 

 was employed as a reagent later on. 



Analyses of leaf-sap of Iris germanica.^ 



In view of the above-mentioned peculiarities of Iris gernianica, it seemed 

 desirable to get an idea of the chemistry of its cells. It is well known that 

 starcli is not stored in the leaves of Iris, except in the guard-cells of the 

 stomata, in which it is by no means invariably present, and in the white bases. 

 In the rhizome and cortex of the root it is, however, plentiful. 



The sap as pressed is of a very light-brown colour, and is strongly acid, 

 malic acid being present. The absence of tannin is shown fcy the fact tliat 

 the addition of ferric chloride to a portion of the sap,' decolourized with 

 animal charcoal, gave only the faintest darkening. Phenyl glucosazone was 

 obtained in abundance from the sap, thus proving the presence of glucose 

 in the usual manner, and on cooling the reaction-mixture a brownish sediment 

 slowly settled down ; this was supposed to be phenyl maltosazone, but it was 

 not possible at the time to settle the question. 



It has been shown by Hunger (12) that substances present in the cocoa- 

 nut milk from unripe nuts inhibit the guaiacum oxydase reaction ; these 

 substances he believes to be sugars. I have found an intense direct guaiacum 

 reaction to be given by the sap of Hedera Helix, the analysis of which by 

 the polarimeter showed a large amount of sugar to be present, the rotation 

 amounting to r40° in a 20 cm. tube. A plentiful crop of phenyl glucosazone 

 crystals was obtained also. Accordingly, I am inclined to think the inhibitor 

 in the cocoa-nut is not sugar. However, it seemed advisable to take into 

 account the actual concentration of the sugars in Iris sap. 



' Most of the quantitative analytical work was done in conjunction with Professor H. H, Dixon in 

 connexion with another research. 



