February 27, 1914] 



SCIENCE 



301 



was first given, some 20 years after Grew's 

 work, bj' Rudolph Jakob Camerarius, of 

 Tiibingen. Camerarius fully appreciated 

 the presence of a real problem here. He 

 also had the genius to see that the philo- 

 sophical attempts of manj^ of his immediate 

 predecessors, to discover its solution en- 

 tirel}^ in their own inner consciousnesses, 

 were futile. With the insight of a modern 

 experimenter Camerarius put the question 

 to the plants themselves. The results of his 

 experiments, as reported in the famous 

 letter of 1694 to Professor Valentin, of 

 Giessen, were clear and conclusive. After 

 noting that aborted seeds were produced 

 by isolated — and therefore unpollinated — 

 female plants of Mercurialis, and of the 

 mulberry ; by castrated plants of the castor 

 bean; and by plants of Indian corn from 

 which he had removed the stigmas, Came- 

 rarius gives his interpretation of these phe- 

 nomena. He says (Ostwald "Klassiker," 

 p. 25) : 



In the vegetable kingdom there is accomplished 

 no reproduction by seeds, that most perfect gift of 

 nature, and the usual means of perpetuating the 

 species, unless the previously appearing apices of 

 the flower have already prepared the plant there- 

 for. It appears reasonable to attribute to these 

 anthers a noble name and the office of male sexual 

 organs. 



In the seventy years after Camerarius 

 had proved in this way the existence of two 

 sexes, and the fertilizing function of the 

 pollen in plants, little advance was made. 

 Bradley, of London, Gleditsch, of Berlin, 

 and Governor Logan, of Pennsylvania, 

 confirmed parts of Camerarius 's work, and 

 the great Linnseus accepted the conception 

 of the stamens and pistils as sexual organs 

 as clearly proven, not, be it noted, ^y the 

 results of Camerarius 's experiments but by 

 "the nature of plants." 



In 1761, J. G. Koelreuter, of Carlsruhe, 

 published an account of the first syste- 

 inatie attempt that had been made, with 



either plants or animals, to produce and 

 carefully study artificial hybrids. In his 

 work with hybrid tobaccos, he demonstrated 

 that characters from both parents are often 

 associated in a single offspring. He thus 

 not only completed Camerarius 's work, but 

 also, by showing that the male parent par- 

 ticipates in the makeup of the offspring, 

 he helped materially to break down the 

 "emboitement theory" of Christian Wolff, 

 which assumed that the embryo came en- 

 tirely from the egg, and that its char- 

 acters could not be influenced by the male 

 parent. It is true that Koelreuter was mis- 

 taken in believing that fertilization is ac- 

 complished by the mingling of the oil on 

 the pollen grains with the secretion of the 

 stigma to form a mixed fluid, which he 

 supposed then penetrated to the ovule. 

 Nevertheless, his conception of the min- 

 gling of two substances was a more with 

 the proper trend. 



Koelreuter also demonstrated that in 

 nature the pollen necessary to fertilization 

 is often brought to the stigma by insects. 

 He thus opened up a field of research which 

 was cultivated with such splendid effect by 

 Konrad Sprengel thirty years later, and by 

 Darwin, Miiller and others a century after- 

 ward. 



In spite of the absolutely conclusive work 

 of Camerarius, Koelreuter and Sprengel 

 on the sexuality of plants, their conclusions 

 were often rejected during the first half of 

 the nineteenth century. Certain devotees 

 of the nature philosophy, for example, 

 occupied themselves either in proving over 

 again, after Cesalpino, that plants can not 

 be sexual, because of their nature, or in 

 trying, by ill-conceived, and carelessly 

 performed "experiments," to prove the 

 conclusions of Camerarius and Koelreuter 

 erroneous. These objectors were finally 

 silenced, however, when Gaertner, in 1849, 

 published the results of such a large num- 



