144 REPORT OF THE CONFERENCE ON GENETICS. 
A cross between a hoary and a glabrous stock, whatever the flower 
colour, gives a simple Mendelian result. I’, is all hoary; F, shows a 
mixture of hoary and glabrous in the ratio of 8 hoary: 1 glabrous or 
1 hoary: 1 glabrous, according as F, is self-fertilised or crossed back 
with the original glabrous form. ‘Taken by themselves these results 
might lead us to suppose that the surface character is determined by a 
single factor, which when present produces hoariness; when absent, 
glabrousness. But unsuspected complexities lie behind this apparently 
simple Mendelian result, and further investigation shows that it cannot be 
represented by so simple an expression. For though we find that any 
hoary x any glabrous gives all hoary, and that such hoary crossbreds x 
self give 8 hoary: 1 glabrous, yet certain glabrous strains when crossed 
together also give all hoary. This latter fact would be inexplicable did 
glabrousness merely consist in the absence of a hoary factor. But before 
treating further of the results obtained from the interbreeding of glabrous 
strains a word must be said about flower colour. The flower colour in 
stocks may be due to one or both of two distinct causes, viz. colour in 
the cell-sap and colour in the special cell constituents—the plastids. 
Non-sap-coloured forms are white or cream according as the plastids are 
uncoloured or of a pale yellow. Sap-coloured forms are of various shades 
of red and blue; those with colourless plastids may be termed self sap- 
colours in contradistinction to the dicolowrs in which both sap and 
plastids are coloured. In both forms the character of the plastids is 
masked by the sap-colour except in the centre of the flower where the 
ground is white in the selfs, cream-coloured in the bicolours. Now when 
glabrous strains (“ wallflower-leaved ” forms of florists) are bred together 
the results, briefly stated, are as follows : 
il Any glabrous sap-colour x any glabrous sap-colour 
I’, =All glabrous sap-coloured 
F,=All glabrous sap-coloured 
2. Any glabrous sap-colour x a glabrous non-sap-colour 
(i.e. white or cream) 
I’, =All hoary sap-coloured 
F,=9 hoary sap-coloured : 3 glabrous sap-coloured : 4 glabrous non-sap- 
coloured. 
3. Glabrous white x glabrous cream 
I’, = All hoary sap-coloured 
F,=9 hoary sap-coloured : 7 glabrous non-sap-coloured 
It has already been shown that the idea of a single factor, which, if 
present produces hoariness, if absent glabrousness, cannot apply here, for 
on such a view it should be impossible to obtain hoary offspring when 
both parents are glabrous. Neither can it be that in cach glabrous strain 
one or other of two complementary factors is present, and that in certain 
\Weterier, 
