THE EXPERIMENTAL STUDY OF GENETIC RELATIONSHIPS

Abstract

The earliest experiment designed to determine the genetic relationships of a plant was carried ouit by Linnaeus and recorded in his famous disquisition on the sex of plants. He tells us that late in the autumn of I757 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 porrifoli'us 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. porrifolius. The hybrid seeds thus obtained were planted in the fall and gave plants which were found to be identical with Tragopogon hybridius. 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 conception had changed greatly since the publication in Fundamenta Botanica (I735) of the oft-quoted clictum, Species tot numeramus, quot diversae formae in principio sunst 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 (I737), 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