96 PRESENT-DAY GARDENING 



done his best to solve any enigmas that he meets, it may be 

 as well to mention some of the difficulties which remain 

 unsolved with regard to the Iris. 



One very interesting problem lies in the determination 

 of the factors that produce the colour of the flower. Re- 

 search on Mendelian lines into the colours of flowers 

 has led to the discovery of the factors in such flowers as 

 Primula sinensis, but Irises seem to be peculiar in that the 

 colours of the flowers of an individual plant are apt to vary 

 from year to year, especially in the case of purples and 

 yellows. For instance, plants of /. cham&iris, bosniaca, 

 serbica, Talischii, which are picked out one year for the 

 clearness of their yellow colour, may in the following season 

 be entirely spoilt, from the garden point of view, by the 

 appearance of purple veins and streaks, which give the pure 

 yellow a muddy appearance. Stranger still, perhaps, are 

 the instances, rare, but not unknown, where one segment 

 of a flower is purple on one side, and yellow on the other, 

 of the centre line. 



It seems as though there is underlying these changes 

 a delicate chemical question. For instance, a solution of 

 purple colouring matter from Iris flowers is changed by 

 addition of a solution of lime into bright yellow, and the 

 question of its origin and nature is probably very intricate. 

 It would, however, be a great gain to know what the 

 determining factors are, for then we might be able, by 

 making suitable additions to the soil in which the plants are 

 grown, to have at will purple or yellow flowered forms of 

 certain Irises, or, at any rate, eliminate from our gardens 

 those dingy yellow flowers, which sooner or later appear on 

 those plants which, in a former year, we have picked ou* 



