In Pursuit of the Gene

84 ¨ PANGENES
peared in April 1900, now reported a 3:1 ratio of hairy to hairless progeny—
the expected ratio under the 1:2:1 law of pangenes for traits determined by
two pangenes. 25 Somehow, in the period between the lecture and the writing
of the manuscript, De Vries appeared to have become certain that the
1:2:1 law was correct, and therefore reported the expected 3:1 ratio of hairy
to hairless. What had precipitated the revision of the ratio?
Early in 1900, just before his father’s death in March, De Vries was sent
an obscure reprint entitled Experiments on Plant Hybrids, written by a Moravian
monk in 1865. The paper had arrived from his old friend and colleague
Martinus W. Beijerinck, who was one of the first to develop the modern
idea of the virus, which he described as an heritable infectious agent, and whose
1882 paper on crossing had first piqued De Vries’s interest in hybridization
experiments. 26 In his paper, Beijerinck had noted that the offspring of hybrids
sometimes showed the parental types and other times produced entirely
new forms. In fact, De Vries’s debt to Beijerinck was reflected in his
Royal Horticultural Society address, which was first titled “Hybridization as
a Means of Pangenetic Infection” and only later amended to “Hybridizing of
Monstrosities.” 27
From many other sources, an obscure reprint, which was thirty-five
years old and written by a complete unknown, might not have claimed De
Vries’s attention, but De Vries was predisposed to listen to Beijerinck. In his
cover letter, Beijerinck wrote, “I know that you are studying hybrids, so
perhaps the enclosed reprint of the year 1865 by a certain Mendel which I
happen to possess, is still of some interest to you.” 28 Several of the remarkable
features of Mendel’s paper would have jumped out at De Vries the moment
he started reading. In fact, much of the experience of reading it must
have been a kind of déjà vu, for Mendel had zeroed in on the key feature of
pangenes.
Like De Vries, Mendel had assumed that an organism could be broken
down into different traits that each corresponded to an individual hereditary
factor, and that these factors were shared among many different organisms
and could be transferred independently from one to another by
the process of hybridization. Both men had suggested that the factors
might come in alternative forms, and that one form could overpower the