SEXUALITY IN PLANTS 



Observed But Not Understood by Babylonians and Assyrians — Not Proved 



Experimentally Until Seventeenth Century — Early Observers Hampered 



by Lack of Proper Methods — Evolution of the Problem 



Largely Due to a Few Great Men/ 



Duncan S. Johnson 

 Professor of Botany, Johns Hopkins University, Baltimore, Maryland. 



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 con- 

 currence of two individuals in the pro- 

 duction of offspring was, in the case of 

 animals, 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 animals than had been familiar to 

 Assyrians, Egyptians and Greeks twenty 

 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 

 Pfefifer on the chemoatactic response of 

 spermatozoids. Of more recent work 

 we may cite that of the plant cytologists 

 on apogamy and apospory, on multi- 

 nucleate 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 knowledge that we now 

 possess concerning the reproductive 

 process in plants. Because of exigencies 

 of time and patience, I shall confine 

 myself primarily to an attempt to 

 picture the chief steps by which our 

 present knowledge of the essential 

 sexual process, the union of two parental 

 substances, has been attained. Inci- 

 dentally, we may note the changes in 

 point of view of investigators 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 phenomena dis- 

 covered in such a way as to indicate the 

 sequence of discovery, within each 

 group, of the different phases of the 

 sexual process, though the order of 

 discussion may thus not always accord 

 with the sequence of the discovery of 

 individual phenomena in plants as a 

 whole. 



WORK OF GREAT MEN. 



In following the evolution and change 

 in aspect of our problem we shall often 

 find it best to keep a few relatively great 

 names prominent. This will serve in 

 the first place to make the story more 

 vivid and intelligible. It will at the 

 same time often come nearer the essen- 

 tial truth, for in each great forward step 

 some one worker has usually been the 

 dominating leader. 



The first discoveries pointing to the 

 existence of sex in plants were evidently 

 made very early in human history by 



^ Address of the vice-president and chairman of Section G, Botany, American Association for 

 the Advancement of Science, December, 1913. (This address, in its complete form, was pub- 

 lished in Science, N. S., Vol. XXXIX, pages 299-319, 1914.) The illustrations have general 

 bearing on the subject discussed and were selected as being more readily intelligible than the 

 detailed technical drawings of the early investigators, whose works are referred to. 



