1912. J Inheritance of Heaviness in Stocks (Matthiola). 545 



according as the combined contribution of ovule and pollen grain includes 

 in every case the four factors (C, B, H, K) necessary for the production of 

 hoariness and sap-colour, or does so in the case of only some pairs of gametes, 

 or in none. 



6. No prediction can be made in regard to an F x thus bred until some 

 cross-breeding test has been applied to the parents, since the result may be 

 affected by factors whose presence in the parents is not revealed by their 

 appearance, and which only become effective on crossing. 



7. "When Fi from unions between glabrous plants is all glabrous, all later 

 generations derived from Fi will also be glabrous. 



8. When Fi from such matings is all hoary, F 2 will be mixed, the 

 proportion of hoary and glabrous individuals depending upon whether the 

 Fi crossbred is heterozygous in 2, or 3, or all the 4 factors for hoariness and 

 sap- colour. 



9. The expectation in the case where Fi is heterozygous — 



In 2 of these factors will be an excess of hoary ( 9 hoary : 7 glabrous). 

 „ 3 „ „ „ glabrous (27 „ : 37 „ ). 



„ 4 „ „ „ „ (81 „ : 175 „ ). 



10. These same ratios may also appear in F 2 when a hoary and a glabrous 

 plant are bred together, since here also the Fi crossbred may be hetero- 

 zygous in 2, 3, or 4 of the factors C, E, H, K. In this form of union, 

 however, it is also possible for Fi to.be heterozygous in respect of only one of 

 these factors, and in such a case the ratio in F 2 will be 3 hoary : 1 glabrous. 



These experiments were carried out in one of the allotment gardens of 

 the Cambridge Botanic Garden. The expense incurred during the progress 

 of the work has been in part defrayed by a grant from the British 

 Association for the Advancement of Science, and also from the Gordon 

 Wigan Fund. 



