i66 BREEDING 



according to the factors in the two cells uniting 

 in each case. We have now to consider what will be 

 the nature of the plants which develop from these 

 fertilised ovules. Let us deal, first, with the first and 

 last on the list. It may be supposed that the Tall- 

 Tall type will develop into a pure tall, and that 

 the Dwarf-Dwarf will produce a dwarf, inasmuch as 

 this was the theory of the reproduction of tails and 

 dwarfs with which we started. Anyhow, we shall 

 see how this supposition fits the facts. 



Now, with regard to the second and third types 

 of union on the list. It should be remembered that 

 the character written first in each pair is that borne 

 by the ovule, and the character written second 

 that borne by the pollen grain. The Tall- Dwarf 

 couple, therefore, was produced by pollinating a pistil 

 on a tall plant with pollen from a dwarf; and the 

 Dwarf -Tall couple by pollinating a pistil on a dwarf 

 plant by pollen from a tall. Now, we know that in 

 the case of this character reciprocal crosses are iden- 

 tical ; that is to say, that the result of both of these 

 crosses is a hybrid tall plant. We are, therefore, now 

 in a position to say what will be the average result of 

 the random union of a large number of ovules, 50 per 

 cent, of which bear the factor for tallness and the 

 other 50 per cent, the factor for dwarfness, with a 

 similar number of pollen grains containing similar 

 factors in the same proportions. By " random " I 

 mean that germ cells bearing a particular factor do 

 not show a preference for germ cells bearing a par- 

 ticular factor, whether similar or dissimilar. 



