Abstract

One of the lecture plates in the collection of the Museum of the University of Amsterdam, generally believed to be used by the Dutch botanist Hugo de Vries, has aroused much discussion in relation to the question of whether or not de Vries knew Mendel's laws before he published his rediscovery of them in 1900. The plate suggests that de Vries observed Mendelian segregation ratios in 1895 and 1896 in the progeny of a cross of two varieties of Papaver with different flower colour. According to his own account, it was through this cross that he first deduced the laws of Mendel in 1896. Some researchers have accepted the lecture plate as proof for this claim. My conclusion is that the plate was not made before 1900 but in 1904 for a lecture course in the USA and, as a consequence, that it is not a contemporary piece of evidence. A closer look at the descriptions of the depicted experiment in de Vries' publications revealed that its original goal was not to investigate segregation but to transfer a monstrosity. The segregation of the flower colour was a accidental event. No research notes of the experiment have survived, but a note on an experiment with Veronica, performed in the same successive years as the Papaver experiment and definitely intended to investigate the segregation of flower colour, shows that this experiment was interpreted in a theoretically conceived, more or less Mendelian way. Because of a sloppy performance, no firm conclusions could be drawn from the experiment, but de Vries clearly had the idea of Mendelian segregation in 1896. That he never brought it up before 1900 suggests that he could not establish the general validity of segregation rules, as is shown in the case of Veronica. The reading of Mendel's paper in 1900 immediately put an end to de Vries' doubts. He scrapped the failures and kept the successes, proudly presenting these to the public as proof for the laws of segregation and, at the same time, of the independence of his discovery