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capable of j^ermiiuitiun could be formed witliout the aid of i)olleii, and all 

 historic records conciir in proviiig that Ifudolpli Jacob Camerarius was the 

 first to attempt to solve the problem in this way. Dioecious plants were 

 cultivated apart from each other, but no perfect seeds were formed. He 

 removed the stamens from the flowers of the castor oil plant and the 

 sti.srmas from maize, with the result that no seeds were set in the castor 

 oil plant, and in the i)lace of grains of corn only empty husks were to be 

 seen. The results of Camerarius were published in 1091-94. At this time 

 the authority of the ancients was so great that Camerarius thought it neces- 

 sary to insist that the \iews of Aristotle and 'J'heophrastus were not op- 

 posed to the sexual theory. Among the few experiments carried out in the 

 next fifty years were those of the Governor of Pennsylvania, James Logan, 

 an Irishman by birth. Logan exi)erimented with some plants of ulaize. 

 Upon a cob from which he removed some of the stigmas, or silks, he found 

 as many grains as there were stigmas remaining. One cob which was 

 wi'apped in m\islin before tlie silks appeared, produced no kernels. In 1751, 

 Gleditsch, director of the botanic garden in Berlin, had been told that a 

 date palm eighty years old, which liad been brought from Africa, never 

 bore fruit. As there was no stanunate tree of the species in Berlin. Gled- 

 itsch ordered pollen sent from Ijcii^ig. The .iourney required nine days, 

 and although Gleditsch thought the pollen spoiled, the male infiore.scence 

 was hung upon the Berlin tree, with the result that seeds were set which 

 germinated in the follov^^ing spring. 



The century following the discovery of Camerarius was characterized 

 by two lines of investigation which, more than any other activity of bot- 

 anists, led to the complete establishment of the sexual theory. I refer to 

 the refutation of the old theory of evolution together with the birth of the 

 doctrine of epigenesis, and the discovery of hybridization ; the first of these 

 being the outcome of microscopic studies, and tlie latter that of experimen- 

 tation. It may be said in this connection that the history of biological 

 science teaches that the greatest and the most substantial progress has 

 been made where the studies of the morpliologist and of the experimenter 

 have gone on side by side, the one serving as a control upon the other. 

 According to the old theory of evolution, or the inclusion theory, that the 

 germ in every seed, for example, contained all the parts of the organism, 

 and that this germ enclosed a similar one in miniature, and so on, like a 

 box within a box. This view of the inclusion of germ within germ was 

 very prevalent in the ISth century, and Kaspar Friedrich Wolf (1759) has 



