R. P. Gregory 103 



only small quantities of pollen. A very common character of the " Ivy-leaf" is 

 that the axis of the inflorescence forms a more or less conical elongation above 

 the whorl of pedicels, at the apex of which carpellary structures may be 

 developed, or ovules may be borne on an exposed disc, which is sometimes 

 surrounded by small lobed expansions (probably carpels) each terminating in a 

 knob resembling a stigma ^ In extracted Fg-forms with green stigmas these 

 expansions are green, in those with red stigmas they are coloured. 



Outline of the inheritance of flower-colour. 



When a plant with fully coloured stems and flowers is crossed with 

 the albino " Snowdrift," the F^ consists of 



Full-colours, " Sirdars," Pale colours and Whites 



in the ratio of 9 full : 3 "Sirdar" : 4 pale colour and white. Although 

 the number of whites recorded in these F^Q is somewhat less than 

 1 in 16, there can be no doubt, I think, that this represents the 

 proportion in which they really occur*. 



In a family of this kind, the plants having fully coloured stems 

 always have fully coloured flowers ; that is to say, the full colour, when 

 present, is distributed throughout the whole plant. Consequently, it 

 is not necessary in this case to draw a distinction between stem-colour 

 and flower-colour, since the colour of both behaves as a single unit'. 

 The inheritance of the full colour, then, follows the scheme outlined in 

 the case of stem-colour (p. 96), in which the relation of the " Sirdars " 

 to the full colours is also explained. 



The place of the pale colours in the scheme must be left undecided 

 until further data are available. It may prove that they constitute an 

 independent series of colours, comparable with the faint stem-colours 

 in their relation to the full colours ; or they may perhaps result from 

 the resolution of the combination of factors to which the full colour 



1 The structures described by Mr L. Crawshay in a malformed Primula (Journ. Roy. 

 Hort. Soc. XXXVI. 1910, p. xxix) are apparently of the same nature. 



' The discrepancy is almost certainly due to the difficulties attending the separation 

 of the pale colours from the whites. The fact that we have sometimes detected a trace of 

 colour in pure " Snowdrift," when the plants have been kept cool, points in the same 

 direction. 



' Keeble and Pellew's experiments (Journ. Genetics, Vol. i. 1910, p. 1) indicate that in 

 certain pigmented forms one, at least, of the factors which determine the production of 

 colour may be absent from the flowers, which are then white, though it is present in the 

 stem, which is therefore coloured. This evidence that, in certain cases, the factors for 

 colour are not distributed throughout the whole plant, is indirectly supported by the 

 results of my experiments with the red-stemmed dominant white "Primrose Queen" 

 (pp. 116, 123). 



