THE FLOWER 229 
this: If two parents differing in some fixed characteristic 
be crossed, the entire offspring, in the first generation, will be 
like the parent possessing the dominant quality. Ii all the 
seed of this generation is planted and carefully protected 
from foreign pollen, its offspring composing the second 
generation from the parents will vary in the proportion of 
# dominants (D, D’, line 2 of the diagram) to j recessives (R). 
Planting all the seeds of the second generation and carefully 
shielding their progeny from foreign pollen, we get from D, 
line 2, all pure dominants (D, line 3) — that is, plants pro- 
ducing only their own type, and from R, line 2, all pure 
recessives (f, line 3). But from each of the two sets of dom- 
inants, D’D’, line 2, marked “ impure ”’ in the diagram, and 
so called because their seeds may produce both dominants 
and recessives, we get the same resuit as in the second gen- 
eration, namely: pure dominants (D’D’, line 3), pure reces- 
sives (R’R’, line 3), and impure dominants (D’’D’’, D’ D”, line 
3). If it were possible to distinguish the seeds of these im- 
pure dominants before germination and plant them only, for 
no matter how many generations, the result would always be 
approximately the same,— } pure dominants, + pure reces- 
sives, and ? impure dominants capable of producing both 
dominants and recessives in the proportion of 3:1. 
259. Practical applications.— Four principles of great 
importance to plant breeders follow from this law in cases to 
which it applies: (1) the absence of variation in the first 
generation of hybrids is no sign that it may not occur later; 
(2) pure recessives always breed true; hence, if they show 
the desired character, no further selection is necessary for 
that character; (3) pure dominants always breed true, but 
the distinction between pure and impure is usually not 
apparent in one generation; (4) the descendants of ‘ im- 
pure ” parents cannot be depended upon to come true to 
either type, but impure dominants may breed recessives, and 
vice versa, with the presumption, however, of 3:1 in favor 
of dominants. 
