so 



IRISH GARDENING 



take place, equal numbers of each of these four 

 kinds will be produced; and, since R w and 

 w R are the same, that means that one plant 

 will start off with RR for two with Rw, for one 

 with w^v. Thus : — 



RR 

 1 



Rw 



2 



WW 



1 



That means again that one plant will be 

 pure for roundness for two hybrid for one 

 pure for ^\Tinkledness— that is, ',the plants 

 produced by the hybrids should be in kind and 

 number exactly as Mendel foinid them to be. 



Consider now what should happen if hybrids 

 in the two pairs of characters, roundness and 

 wrinkledness, and yellow albumen and green 

 were mated. 



The materials given off by any hybrid may be 

 represented thus : — 



In the pollen : In the ovary : 



R R 



So far as roundness and wrinkledness are con- 

 cerned, there should be equal numbers of plants 

 starting off with the materials. 



RR, or Rw, or wR, or ww. 



But in each of those kinds there ought also 

 to be equal numbers starting off with the 

 materials — 



YY, or Yg, or gY, or gg. 



If we consider those starting off with RR, there 

 should be one starting off also with YY for one 

 with Yg, for one with gY, for one with gg. 

 That is to say, if there were four plants starting 

 off with RR, these four plants should have 

 equal chances of carrying also YY or Yg or gY 

 or gg ; and the full materials carried by the 

 four plants would have equal chances of being 

 as follows : — 



RR 

 YY 



RR 



Yg 

 RR 

 gY 

 RR 



these kinds were similarly affected as to the dis- 

 tribution of the materials Y and g, the materials 

 carried off by the whole sixteen plants would be 

 as follows : — 



Nine plants in sixteen- — those in the left 

 upper part of the diagram— would be round with 

 yellow albumen ; three — those below — would 

 be round with green albumen ; Ihree — those 

 in the right upper portion of the diagram- 

 would be wrinkled with yellow albumen ; and 

 one would be 'u'rinkkd with green albumen. 

 And one only in each of the four kinds — those 

 at the four corners — would breed true. 



Set out otherwise there should be — 



That is, again, the plants produced should be 

 in kind and proportional numbers exactly as 

 Mendel found them. Not only so, but the 

 proportions of pure-breeding plants in each kind 

 should be exactly as Mendel found. 



Mendel himself did not trouble about the 

 theoretical proof, but went on to prove his 

 theory experimentally, and, as the theoretical 

 proof is absolutely good, we shall content our- 

 selves with giving only one of his experimental 

 proofs. 



He mated the hybrids between round peas 

 having yellow albumen and wrinkled peas having 

 green albumen with both their parents. We 

 shall take the case in which the hybrids were 

 mated with wrinkled parents having green albu- 

 men. In this case the materials offered were — 



By the pure parents By the hybrids. 



R 



w w 



But the plants starting off with Rw, wR, and 

 WW would be similarly affected as to the dis- 

 tribution of the materials Y and g. Thus, if 

 there were sixteen plants in all — that is, four of 

 each kind RR, Rw, wR, and ww, and each of 



So far as the round and wrinkled materials are 

 concerned, the materials av in the pure parents 

 have equal chances of mating with R or w in 

 the hybrids. Thus there ought to be produced 

 equal numbers of seeds with the materials Rw 



