254 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



later work to be regarded as only a convenient method of 

 describing the locality of the enzyme. It is the writer's 

 view (1914, 1) that all the differences in reaction can satis- 

 factorily be explained on the supposition that a-naphthol 

 is more sensitive to the inhibitors of the petal than is 

 benzidine. In support of this is the fact that in certain 

 Iris flowers treatment with hydrogen cyanide resulted in 

 the removal of inhibitors, after which the benzidine reaction 

 was given with greater intensity, and a-naphthol, pre- 

 viously oxidized only in the veins, afforded a dark blue 

 colour in the epidermis also. In other varieties of Iris 

 the two reagents were vigorously acted upon in both epider- 

 mis and veins, when the reagents, including hydrogen per- 

 oxide, were applied directly to the freshly gathered flowers. 

 Keeble and Armstrong (1912) found that tissues contain- 

 ing anthocyan pigments always afforded peroxidase reac- 

 tions, and very frequently contained organic peroxide also. 

 Since the latter (and to a lesser degree the former also) 

 varies in quantity according to the amount of light to 

 which the tissue containing it has been subjected, they do 

 not regard its absence at a given time as of any great im- 

 portance. As the distribution of peroxidase greatly ex- 

 ceeds that of sap pigment, they concluded that the presence 

 or absence of chromogen, not of peroxidase, is a Mendelian 

 unit. They point out that, if two factors were involved in 

 the production of pigment in a red-stemmed variety of 

 Primula sinensis investigated by them, it ought to be 

 possible to obtain two types of green-stemmed plants 

 viz., one lacking chromogen, and another lacking the 

 oxidase system. Only one kind has, however, been found. 

 The results of crosses are shown here, adopting the usual 

 symbols, C for chromogen, and O for oxidase: 



Green stemx reddish stem^OcxOC, 

 and F 



