300 



SCIENCE 



[N. S. Vol. XXXIX. No. 1000 



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 pict- 

 ure the chief steps by which our present 

 knowledge of the essential sexual process, 

 the union of two parental substances, has 

 been attained. Incidentally 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 group- 

 ing the chief phenomena 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 sequence, in time, of the 

 discovery of individual phenomena in 

 plants as a whole. 



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 in- 

 telligible. It will at the same time often 

 come nearer the essential truth, for in 

 each great forward step some one worker 

 has usually been the dominating leader. 



i. the discovery that pollination is a 

 pr£kequisite to seed-formation. 

 750 B.C. TO A.D. 1849 

 The first discoveries pointing to the exist- 

 ence of sex in plants were evidently made 

 very early in human history by peoples 

 cultivating unisexual plants for food. The 

 existence of fertile and sterile trees of the 

 date palm, e. g., was known to the peoples 

 of Egypt and Mesopotamia from the 



earliest times. Eeeords of the cultivation 

 of these trees and of artificial pollination 

 have come down to us on bas-reliefs from 

 before 700 B.C. found in the palace of 

 Sargon at Khorsabad (Haupt and Toy, 

 1899). The Assyrians, it is said, commonly 

 referred to the two date trees as male and 

 female (Rawlinson, 1866). The Greeks, 

 in spite of their peculiarly keen interest in 

 natural phenomena, failed to offer any 

 definite interpretation of this well-known 

 fact concerning the date palm. Aristotle 

 and Theophrastus report the fact, gained 

 apparently from the agriculturalists and 

 herb-gatherers, that some trees of the date, 

 fig and terebinth bear no fruit themselves, 

 but in some way aid the fertile tree in per- 

 fecting its fruit. But without recording a 

 single crucial experiment on the matter, 

 Theophrastus , concludes that this can not 

 be a real sexuality, since this phenomenon 

 is found in so few plants. 



In this uncertain state the knowledge of 

 sexuality in plants was destined to rest for 

 twenty centuries, waiting for the experi- 

 mental genius of Camerarius to give a con- 

 clusive answer to the question raised by the 

 Assyrian and Greek gardeners and an- 

 swered wrongly by Theophrastus. The 

 English physician Grew (1676) did, it is 

 true, accept and expand the suggestion of 

 Sir Thomas Millington that the stamens 

 serve as the male organs of the plant. Thus 

 Grew concludes (p. 173) that when the 

 anther opens the "globulets in the thecse 

 act as vegetable sperm which falls upon the 

 seed-ease or womb and touches it with pro- 

 lific virtue." But this guess, though it 

 proved correct in the main point, was still 

 a guess, and not supported by any critical 

 evidence so far as recorded by Grew. The 

 only adequate evidence that could be ob- 

 tained on this question, while microscopes 

 and technique were still so imperfect, was 

 experimental evidence. This kind of proof 



