THE EXPERIMENTAL STUDY OF GENETIC RELATION- 
SHIPSi 
H. H. Bartlett 
The earliest experiment designed to determine the genetic relation- 
ships of a plant was carried out by Linnaeus and recorded in his famous 
disquisition on the sex of plants. He tells us that late in the autumn of 
1757 he stumbled upon some plants of Tragopogon hybridus in the 
botanic garden at Upsala, growing in a bed where only Tragopogon 
pratensis and Tragopogon porrifolius had been planted. Before this 
time, as we know from Hartmann's dissertation on hybrid plants, 
Linnaeus had thought it possible that Tragopogon hybridus was a 
cross between Tragopogon porrifolius and Lapsana stellata — species of 
two quite unrelated genera. Now, however, he had a clue to its true 
relationship, which he set about to prove. The next year he removed 
the pollen from some heads of the yellow-flowered Tragopogon pratensis 
and sprinkled the styles with pollen from the purple-flowered T. por- 
rifolius. The hybrid seeds thus obtained were planted in the fall and 
gave plants which were found to be identical with Tragopogon hybridus. 
The flowers were not completely purple, as in the staminate parent, 
but showed the influence of the pistillate parent in their yellow bases. 
After this experiment, Linnaeus tells us, it was impossible to doubt 
that new species might come into being by hybridization. His con- 
ception had changed greatly since the publication in Fundamenta 
Botanica (1735) of the oft-quoted dictum, '^Species tot numeramus, 
guot diversae formae in principio sunt creatae.'' (Every species which 
we can enumerate was created in the beginning a distinct form.) 
The more mature views of Linnaeus, however, were in advance of 
his time. Philosophia Botanica (1737), in which the doctrine of 
special creation was set forth, continued, long after his death, to be the 
vade mecum of botanists. The conception of the hybrid origin of 
species was so completely disregarded that Sir James Edward Smith, 
an ardent Linnaean, the possessor of the Linnaean herbarium and 
1 Invitation paper read at the symposium on "The Genetic Relationship of 
Organisms" before the Botanical Society of America at Philadelphia, December 30, 
1914. 
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