October io, 1912] 



NATURE 



i«i 



either by destroying peroxydase or by setting up con- 

 ditions under which the activity of peroxydase is 

 arrested. Assuming further that the inhibitor acts in 

 the latter way, it follows that if means of destroying 

 or removing the inhibitor be discovered and employed, 

 the peroxydase released from the inhibitory grip 

 should be free to effect the oxidation of our reagents. 



This train of reasoning gave us a point of departure 

 for experiment. Starting from this point Dr. Arm- 

 strong and I have found in hydrogen cyanide a means 

 of removing peroxydase-inhibition. Thus if dominant 

 white fiowers are immersed in a o'4 per cent, solution 

 of hydrogen cyanide for twenty-four hours, washed, 

 and treated with either of our reagents together with 

 hydrogen peroxide, pronounced peroxydase reactions 

 are obtained, both in the epidermal and bundle tissues 

 of the corolla. Carbon dioxide in aqueous solution 

 produces a like, albeit a less pronounced effect. 



Now, it so happened that we had at our disposal 

 a race of primulas, the flowers of which lend them- 

 selves peculiarly well to the purpose of confirming 

 these observations. The race in question is char- 

 acterised by blue flowers with fairly symmetrically 

 placed paired white patches on each petal. We have 

 reason to believe from the known ancestry of this race 

 that these white patches are produced by a localised 

 inhibitor. 



Corollas of these flowers treated with a-naphthol or 

 'benzidine become quite colourless. When, however, 

 hydrogen peroxide is added the natural pattern is 

 restored. The parts originally blue are stained lilac- 

 blue or brown, according to the reagent used, and 

 the inhibitory patches stand out as in the intact flower 

 .as white areas on the coloured ground. 



If instead of submitting the parti-coloured flowers 

 •directly to the oxydase reagent they are treated first 

 with hydrogen cyanide, and then treated with the 

 .reagent and subsequently with hydrogen peroxide, 

 the inhibition located in the white areas is found to 

 have been removed, and the peroxydase reaction is 

 produced over blue and white areas alike. 



Hence the Mendelian hypothesis of the inhibitory 

 nature of dominant whites is confirmed by biochemical 

 ■methods. Moreover, these methods demonstrate that 

 the inhibitor acts not by destroying but by preventing 

 the action of oxydase upon the chromogen. 



There are many other aspects presented by the 

 phenomena of oxydase distribution in P. sinensis and 

 •other plants which we have investigated. Some I 

 may enumerate, but lack of time must be my excuse 

 for not dealing fully with any of them. 



The close proximity in the flower of the superficial 

 and deep oxydases suggests that the latter may co- 

 •operate with the former in producing flower-pigments. 

 This possibility entails the hypothesis of a transloca- 

 tion of oxydase from the region in which it is secreted 

 to that in which it acts, and there are not a few facts 

 which are in favour of this view ; for example, the 

 lines of deep colour which occur along the veins of 

 ■many flowers, the frequency with which the walls 

 of cells appear to contain oxydase, the occurrence of 

 oxydase in the mesophyll cells which adjoin the bundle 

 sheath, and the evidence provided by the mutual in- 

 fluence of stock and scion in grafted plants and in 

 graft hybrids. Though these and other subjects must 

 be passed over, I cannot resist giving what appears 

 to me to be the most elegant mode of demonstrating 

 the relation between oxydases and pigmentation which 

 we have as yet observed. The plant which has served 

 for this purpose is the sweet William (Dianthus har- 

 ■batus), and any " of the old-fashioned races of this 

 plant common in cottage gardens suffices, provided 

 that it be an ever-sporting race. Such a race is 

 known by the fact that it bears, on one and the same 



NO. 2241, VOL. 90] 



head, flowers of different colours. The race which we 

 have used is very sporting, a single plant bearing 

 in one inflorescence deep magenta, pale magenta, 

 white with limited rose flush, and all but pure white 

 flowers. 



If a petal of each of these flowers be treated with 

 the benzidine reagent, it is found that the extent and 

 amount of the oxydase reaction, as measured by the 

 distribution and depth of brown coloration indicative 

 of oxydase, coincide precisely with the extent and 

 amount of pigmentation. The full-coloured petal 

 gives a uniform deep brown reaction, the light 

 magenta a uniform but paler reaction, the petal with 

 a limited rosy flush gives a slight reaction, limited to 

 the pigmented area, and the all-but-white petal gives 

 none but the slightest reaction, and that only in the 

 part of the petal which contained traces of pigment. 

 Thus — unless the results are due to a partial inhibition 

 which has eluded our attempts at demonstration — it 

 would seem established that the ever-sporting habit 

 is due to differences in the amount of oxydase in the 

 diversely coloured flowers. 



The sweet William is also noteworthy in that it 

 contains white races, some of which give an oxydase 

 reaction in their petals, and some of which give no 

 o.xydase reaction. Breeding experiments now in pro- 

 gress will decide whether or no these white races, 

 like those of sweet peas investigated by Bateson and 

 Punnett, mated together yield coloured progeny. If 

 so, the factors for colour, long wandering yet not 

 lost, which meet again in reversionary coloured cross- 

 breeds, may prove to be a chromogen factor and an 

 oxydase factor. 



Finally, a brief reference must be made to our 

 observations on the periodic fluctuation of oxydase 

 in plants. Various observers have noticed that plant 

 tissues give the peroxydase reaction much more gener- 

 allv than the oxydase reaction. The observations now 

 to be described indicate that this is due to the greater 

 stability of peroxydase as compared with the organic 

 peroxide. 



In certain circumstances a tissue which gives only 

 the peroxydase reaction may exhibit the direct oxy- 

 dase reaction. Moreover, the extent of the peroxy- 

 dase reaction, as judged by the depth of coloration 

 of the reagent, varies in similar plants at different 

 times. 



Inquiry into the meaning of these fluctuations led us 

 to the discovery that the nature and amount of oxydase 

 contained in a plant tissue varies in an orderly manner 

 according to external conditions. 



Among the conditions which determine this fluctua- 

 tion are light and darkness. Plants subjected to 

 normal illumination possess less oxydase than those 

 which are kept in darkness. After one or two days' 

 exposure to darkness plants of P. sinensis contain 

 more peroxydase than sister plants kept under normal 

 conditions of illumination. Moreover, after such an 

 exposure to darkness tissues which under normal 

 conditions give only peroxydase-reactions yield distinct 

 oxvdase-reactions. 



Whether these phenomena are general among plants 

 we are not yet in a position to say; but repeated 

 experiment enables us to vouch for them in the case 

 of P. sinensis. Should the results of similar investi- 

 gations with other plants show that this diurnal 

 variation of the oxydase-content of plant tissues is 

 of general occurrence, we may perhaps discover therein 

 the means wherebv many of the phenomena of 

 periodicitv exhibited bv plants are maintained and 

 regulated! We know that the light and darkness of 

 the dav and night set up rhythms in the plant; for 

 example, that the leaves of various plants assume 

 nocturnal and diurnal positions. We know further 



