56 PROBLEMS OF GENETICS 



I imagine in all such examples it will be found that there are 

 indications of irregularity in the distribution of the differ- 

 entiations such as to justify the view that they are not under that 

 geometrical control which governs the normal differentiation 

 of the parts. The question next arises whether these consider- 

 ations apply also to the production of a bud-sport as a rare 

 exception, but by the nature of the case it is not possible to 

 say positively whether the appearance of an exceptional sport 

 is due to the unsuspected presence of a pre-existing fragment of 

 material having a special constitution, or to the origin, de novo, 

 of such a material. For instance one of the garden forms of 

 Pelargonium known as altum is liable perhaps once in some 

 hundreds of flowers to have one or two magenta petals. The 

 normal colour is a brilliant red ; and as we may be fairly sure that 

 this red is recessive to magenta the interpretation would be 

 quite different according as the appearance of the magenta is 

 regarded as due to the presence of small areas endowed with 

 magentaness, or to the spontaneous generation of the factor 

 for that pigment. Either interpretation is possible on the facts, 

 but the view that the whole plant has in it scarce mosaic particles 

 of magenta seems on the whole more consistent with present 

 knowledge. 



In Pelargonium altum the enzyme causing the magenta colours 

 must be distributed in very small areas, but a case in which the 

 magenta is similarly arranged in a much coarser patchwork 

 may be seen in the Pelargonium " Don Juan," which often bears 

 whole trusses or branches of red flowers upon plants having the 

 normal dominant magenta trusses. In most cases there is little 

 doubt that though the magenta flowered parts can " sport" to 

 red, the red parts could not produce the magenta flowers. 



The asymmetrical, or to speak more precisely, the disorderly, 

 mingling of the colours in the somatic parts is thus an indication 

 of a similarly disorderly mixing of the factors for those colours 

 in the germ-tissues, so that some of the gametes bear enough of 

 the colour-factors to make a self-coloured plant, while others 

 bear so little that the plant to which they give rise is a patch- 

 work. If this view is correct we may extend it so far as to con- 



