The Journal of Heredity 



famous letter of 1694 to Professor 

 Valentin, of Giessen, were clear and con- 

 clusive. 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, Camerarius 

 gives his interpretation of these ]jhe- 

 nomena. He savs (Ostwald ' ' Klassikcr , ' ' 

 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 pre- 

 pared the plant therefor. It appears 

 reasonable to attribute to these, anthers 

 a nobler 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, Gled- 

 itsch, of Berlin, and Governor Logan, 

 of Pennsylvania, confirmed parts of 

 Camerarius's work, and the great 

 Linnjeus accepted the conception of the 

 stamens and pistils as sexual organs as 

 clearly proven, not, be it noted, by the 

 results oj Camerarius's experiments but 

 by ''the nature oj plants ^ 



koelreuter's hybrids. 



In 1761 J. G. Koelreuter, of Carls- 

 ruhe, published an account of the first 

 systematic attempt that had been made, 

 with either plants or animals, to pro- 

 duce and carefully study artificial hy- 

 brids. In his work with hybrid tobac- 

 cos, he demonstrated that characters 

 from both parents are often associated 

 in a single offspring. He thus not only 

 comjjleted Camerarius's work, but also, 

 by showing that the male ])arent par- 

 ticijjates in the makeup of the offspring, 

 he helped materially to break down the 

 "emijoitemcnt theory" of Christian 

 Wolff, which assumed that the embryo 

 came entirely from the egg, and that its 

 characters could not be influenced by 

 the male i)arent. It is true that Koel- 

 reuter was mistaken in believing that 



fertilization is accomplished by the 

 mingling of the oil on the ]:)ollen grain 

 with the secretion of the stigma to form 

 a mixed fluid, which he supposed then 

 penetrated to the ovule. Nevertheless, 

 his conception of the mingling of two 

 substances was a move with the proper 

 trend. 



Koelreuter also demonstrated that in 

 nature the pollen necessary to fertiliza- 

 tion is often brought to the stigma by 

 insects. He thus opened up a field of 

 research which was cultivated with such 

 splendid efifect by Konrad Sprengel 

 thirty years later, and by Darwin, 

 M idler and others a century aftenvard. 



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 philos- 

 ophy, 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 erron- 

 eous. These objectors were finally 

 silenced, however, when Gaertner, in 

 1849, published the results of such a 

 large number of well-checked experi- 

 ments, entirely confirming the works of 

 Camerarius, Koelreuter and Sprengel, 

 that no thinking botanist has since 

 doubted the occurrence in flowering 

 plants of a sexuality essentially identical 

 with that found in animals. 



DISCOVERY OF THE POLLEN TUBE 



During the opening years of the nine- 

 teenth century a number of botanists, 

 who believed in the sexuality of plants, 

 tried to discover by the aid of the 

 microscope just how fertilization is 

 eflfected. Most botanists of the day 

 believed the ]X)llen grain burst on the 

 stigina, and that its granular contents 

 found a way through the style to the 

 ovary. An entirely new asjject of tho 

 l)roblem of fertilization was opened up, 

 liowever, when in 1823 Amici, of Mo- 

 dena, saw on the stigma of Portulacca 

 young i)ollen tubes arising from the 

 jjollen grains. Seven \-ears later he 



