182 MENDELISM 
breeding. This conclusion is at least so far firmly 
established that no alternative hypothesis has been 
put forward which will explain the facts. 
We have next to consider what will be the result of 
crossing our cross-bred plants with one another instead 
of with the pure white form. The following possi- 
bilities present themselves : 
A yellow female gamete may pair with a yellow male gamete. 
” ” ” ” white ” 
” 
A white 3 ss ” » yellow - 
” ” ” ” ” white ” 
All these combinations are equally likely to occur, 
because in each plant there are the same number of 
yellow and white female gametes as well as of yellow 
and white male gametes. In the long-run, therefore, 
each of the above pairings will be found to have taken 
place in an equal number of cases. The grains which 
we shall obtain, then, will be yellow and white in colour, 
and the two kinds will occur in the following propor- 
tions: I pure white; 2 white x yellow or yellow x 
white, which, as we have already seen, will be yellow 
in appearance ; and 1 pure yellow. Altogether, we 
shall expect a ratio of 3 yellow grains to 1 white. 
In an actual experiment the following result was 
obtained : 
Yellow grains 16,592, or 74'5 per cent. 
White 4, 5,681, 4, 25°5 ‘a 
—that is to say, a ratio of 2:9 yellow to 1 white. 
The expression 14 :2Aa:i1a, in which A represents 
the dominant character (yellow) and a the recessive 
character (white), may be spoken of as a Mendelian 
