136 MISSOURI BOTANICAL GARDEN BULLETIN 
tribution to the subject of hybridization. Mendel appealed 
to Naegeli, the leading botanist of his time in Germany, but 
Naegeli failed to see the importance of the work, so that 
Mendel’s researches lay buried until the end of the century, 
when the principle was rediscovered by independent workers 
in Germany, Austria, and Holland, and published within 
a few weeks of each other. 
It seems probable that the lack of knowledge of the actual 
factors civelsae in the reproduction of plants prevented the 
realization of the importance of Mendel’s discovery. More- 
over, Mendel was in advance of his time both in his concep- 
tion of the organism and in the methodical way in which 
he attacked this particular problem. Briefly stated, the 
essence of Mendel’s discovery is that in the hybrid offspring 
the different characters of the parents are independentl 
inherited. Previously hybrids had been compared wit 
their parents, organ for organ, the whole plant being treated 
as a unit. Mendel’s method, which has proved so useful in 
modern experimental work, was to compare the races which 
he crossed, character for character, and in this way to study 
the inheritance of each parental difference independently of 
all the others. This result was achieved by confining his 
experiments to plants which differed not in many ways, but 
in a single feature. Thus Mendel crossed peas having yel- 
low seeds with those having green ones, the plants in every 
other respect being alike. As a consequence the inheritance 
of this single character, yellow or green seeds, could then 
be studied in the offspring. By this means the fundamental 
fact was demonstrated that, alaioas a first generation (F,) 
of hybrids produced seed of a uniform color (all yellow), 
the parental difference of green seed reappeared in the second 
generation (F,). This latter fact is now known as the prin- 
ciple of segregation, since the second generation plants, the 
result of self pollinating the hybrid Seats of the first gen- 
eration, produce seeds, some yellow and others green. Simple 
as this fact apes, it is the principle of segregation which 
constitutes Mendel’s chief contribution to the subject. Not 
only does the diversity of parental characters appear in the 
second generation but the two types are in a fairly definite 
Sy gee Mendel obtained from 253 first generation hy- 
brid plants a total of 6,022 yellow seed ane 2,001 green 
seed, which is very close to theoretical expectation, namely, 
a ratio of three to one. ; 
When some of the yellow and green seed thus obtained 
pial a cones it was found that the green seed always pro- 
duced plants bearing nothing but green seed ; in other words, 
this character bred true. But when the yellow seed were 
