308 LOCK: STUDIES IN PLANT BREEDING 
F 2 may also be more concisely written A + 2Aa + a, 
avoiding an unnecessary repetition of letters. This ex¬ 
pression is the formula for F 2 of a Mendelian monohybrid. 
Example I. —Sutton’s Telegraph Pea, with green or 
partly green cotyledons, rarely becoming dull yellow in 
weathered pods, was crossed with a small smooth-seeded 
native pea, having bright yellow cotyledons. From 17 
successful pollinations 50 seeds were produced, the cotyle¬ 
dons of all of which were completely yellow. 41 of these 
seeds gave rise to plants which produced altogether 646 seeds 
(F 2 ), of which 488 had completely yellow cotyledons and 
158 had green cotyledons, the majority being strong bright 
green, but a few showing slightly yellowish patches and thus 
resembling the parent form Telegraph. The yellow and 
green seeds were thus in the proportion 3’09 : 1. 
A considerable number of these seeds were sown, but 
only 44 yellow and 11 green seeds produced plants. The 
latter gave rise to 295 seeds, 291 of them, bright green or 
partly yellowish and 4 quite yellow, but paler than the 
offspring of yellow seeds. Pure bred Telegraph plants 
grown at the same time produced a similar lot of seeds as 
regards colour, but these included a somewhat larger 
proportion entirely dull yellow. This was probably due to 
their having been exposed in the pods rather longer. 
Of the 44 plants derived from yellow seeds, 16 gave rise 
to yellow seeds only, viz., to 1,013 yellow seeds. 28 plants 
produced 1,152 seeds, both green and yellow, 877 being of 
the latter and 275 of the former colour or 3*19 : 1. 
In a further generation a somewhat larger number of 
offspring was obtained, and the previous result again 
confirmed. The seeds of six plants (which had yielded both 
yellow and green seeds in F 3 ) were sown and gave rise to 
the following offspring : — 
Forty-seven green seeds gave rise to plants which bore 
1,325 green seeds only (F 4 ). 
