ON FACT VS. THEORY 
“And that is why those who had devoted their 
lifetimes to counting stamens and classifying 
shapes told me, through their writings, that a cross 
might be made within species, but never between 
species; that is why when I did make a cross 
between species they looked no further into the 
truth, but simply moved up a notch, and said, 
“Very well, but you cannot make a cross between 
genera’; that is why, when I did that very thing, 
not once, but scores of times, that type of scientist 
lost interest in rule making and went back to 
stamen counting.” 
To realize the point more clearly, let us observe 
for a moment the common tomato—which belongs 
to that large division of plants, the nightshade 
family. 
Just as the rose family includes not only the 
rose, but the apple and the blackberry and 
sixty-two other plants, so the nightshade family 
includes seventy-five genera and more than 
eighteen hundred species. 
The classification is built around structural 
facts, such as that plants of this family originally 
had alternate leaves with five stamens and a two- 
celled ovary, or egg chamber, each cell containing 
many eggs. 
These structural similarities in the plants of 
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