54 PROBLEMS OF GENETICS 



metrical system, which to those who have never given special 

 attention to such things before, will often seem surprisingly 

 precise. The arrangement of the leaves on uninjured, free- 

 growing shoots can generally be seen to follow a very definite 

 order, just as do the flowers or the parts of the flowers. If 

 however bud sports occur, then though the parts included in 

 the sports show all the geometrical peculiarities proper to the 

 sport-variety, yet the sporting-buds themselves are not related 

 to each other according to any geometrical plan. 



A very familiar illustration is provided by the distribution 

 of colour in those Carnations that are not self-coloured. The 

 pigment may, as in Picotees, be distributed peripherally with 

 great regularity to the edges of the petals; or, as in Bizarres and 

 Flakes, it may be scattered in radial sectors which show no 

 geometrical regularity. Now in this case the pigments are the 

 same in both types of flower, and the chemical factors concerned 

 in their production must surely be the same. The difference 

 must lie in the mechanical processes of distribution of the pig- 

 ment. In the Picotee we see the orderly differentiation which we 

 associate with normality; in the Bizarre we see the disorderly 

 differentiation characteristic of bud-sports. The distribution of 

 colour in this case lies outside the scheme of symmetry of the 

 plant. 



Such a distribution is characteristic of bud-sports, and of 

 certain other differentiations in both plants and animals, which 

 I cannot on this occasion discuss. Now reflexion will show that 

 these facts have an intimate bearing on the mechanical problems 

 of heredity. For first in the bud-sports we are witnessing the 

 distribution of factors which distinguish genetic varieties. We 

 do not know the physical nature of those factors, but if we must 

 give them a name, I suppose we should call them "ferments" 

 exactly as Boyle did in 1666. He is discussing how it comes about 

 that a bud, budded on a stock, becomes a branch bearing the 

 fruit of its special kind. He notes that though the bud inserted 

 be "not so big oftentimes as a Pea," yet "whether by the help 

 of some peculiar kind of Strainer or by the Operation of some 

 powerful Ferment lodged in it, or by both these, or some other 



