234 MendeTs Laws of Alternative Inheritance in Pea^ 
also exhibit only recessive characters, and Mendel assures us that this was the 
case; of those which exhibit dominant characters, one-third should produce 
apparently pure-bred oflfspring of dominant character, two-thirds should produce 
" hybrid " offspring. The behaviour of plants of the third generation, the offspring 
of plants with dominant characters, is shown in Table II. 
TABLE II. 
Proportion of Plants luith Dominant Characters, among Hyhrids of the Second 
Generation, which transmitted only Dominant Characters to their offspring. 
Characters Crossed 
Number of 
Second Gene- 
ration Hybrids 
observed 
Number which 
transmitted 
only Domi- 
nant Characters 
Theoretical 
number 
Probable 
Error of 
Theoretical 
Expectation 
Deviation 
of observed 
number 
1. (Shajje of Seeds) 
565 
193 
188-3 
+ 7-558 
-f4-7 
2. (Colour of Cotyledons)... 
519 
166 
173 
+ 7-244 
-7-0 
3. (Colour of Seed-Coat) ... 
100 
36 
33-3 
+ 3-180 
+ 2-7 
4. (Shape of Pods) 
100 
29 
33-3 
+ 3-180 
-4-3 
5. (Colour of Pods) 
100 
40 
33-3 
+ 3-180 
-f6-7 
6. (Distribution of Flowers) 
100 
33 
333 
+ 3-180 
-0-3 
7. (Height of Plant) 
100 
28 
33-3 
+ 3-180 
-5-3 
Three of these seven determinations give results which differ from that 
indicated by Mendel's hypothesis by less than their probable errors ; the difference 
between the actual result and that postulated by the hypothesis is equal to the 
probable error in one case, and greater in three cases ; but a discrepancy as great 
as twice the probable error only occurs once. Here again, therefore, Mendel's 
statement is admirably in accord with his experiment. 
Mendel made several series of observations to test the validity of his statement 
in cases involving more than one pair of differential characters. The number of 
possible combinations quickly becomes too great to deal with experimentally, and 
the most complicated case recorded is that of hybrids between female parents of a 
race producing round smooth seeds with yellow cotyledons and grey -brown seed- 
coats, and male parents of a race with angular green seeds and white seed-coats. 
The original hybrids were 24 in number, and from these 639 hybrids of the second 
generation were grown and observed. Denoting the dominant characters, round- 
ness, yellowness, and greyness of seed-coat, by A, B, C, and the corresponding 
recessive characters, angidarity, greenness, and whiteness of seed-coat, by a, h, 
and c respectively, it is clear that the possible combinations of these characters in 
the hybrids of the second generation are the possible combinations of the three sets 
of characters 
AA aA + Aa + aa, 
BB+bB + Bb+ bb, 
CC+ Cc + cC + cc. 
