THE HISTORY OF THE DISCOVERY OF SEXUALITY IN 
PLANTS.? 
By Prof. Duncan 8. JOHNSON. 
From the beginning of man’s thoughtful consideration of natural 
processes, the phenomenon of sexual reproduction, with the associated 
phenomena of heredity, have persistently engaged his keenest interest. 
The primary fact of the necessary concurrence of two individuals in the 
production of offspring in the case of animals was recognized from the 
beginning. ‘The equivalent phenomenon was not established for plants 
until the end of the seventeenth century. At this time, however, little 
more was known of the essential features of the sexual process in ani- 
mals than had been familiar to Assyrians, Egyptians, and Greeks 20 
centuries before. 
Of the additions made since 1700 to our knowledge of sexual 
reproduction, of its varied types and of the associated phenomena, 
no mean share has been contributed by botanical investigators. 
Noteworthy among such contributions are the work of Koelreuter 
and Mendel in the production and systematic study of plant hybrids, 
and the early work of Pfeffer on the chemotactic response of sper- 
matozoids. Of more recent work we may cite that of the plant 
cytologists on apogamy and apospory, on multinucleate sexual cells 
or gametes and on the long-delayed nuclear fusion in the sexual 
reproduction of the plant rusts. It should then be of interest for us 
to consider just how and when the more important steps have been 
taken in building up the vast mass of somewhat incomplete knowl- 
edge that we now possess concerning the reproductive process in 
plants. Because of exigencies of time and patience, I shall con- 
fine myself primarily to an attempt to picture the chief steps by 
which our present knowledge of the essential sexual process, the 
mingling of two parental substances, has been attained. Incidentally 
we may note the changes in point of view of investigatcrs and in 
their mode of attack on this problem. I shall attempt to suggest the 
trend of development more clearly by often grouping the chief phe- 
nomena discovered in such a way as to indicate the sequence of dis- 
covery within each group of the different phases of the sexual process, 
though the order of discussion may thus not always accord with the 
1 Address of the vice president and chairman of section G, Botany, American Association for the Ad- 
vancement of Science, December, 1913. Reprinted by permission of author. Printed in Science, Feb. 
27, 1914. 
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