oi 



capable of germination could lie fonued without tlie aid of polleu. and all 

 historic records concur in proving that Rudolph Jacob Camerarius was the 

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

 cultivated a])art from each other, but no perfect seeds were formed. He 

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

 stigmas from maize, with the result that no seeds were set in the castor 

 oil plant, and in the place of grains of corn only empty husks were to be 

 seen. The results of Camerarius were published in 1691-94. At this time 

 the authority of the ancients \A'as so great that Camerarius thought it neces- 

 sary to insist that the Aiews of Aristotle and Theophrastus were not op- 

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

 next fiftj- years were those of the Governor of Pennsylvania, James Logan, 

 an Irishman by birth. Logan experimented with some plants of maize. 

 I pon a cob from which lie removed some of the stigmas, or silks, he found 

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

 wi-apped in muslin before the silks appeared, produced no kernels. In ITol, 

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

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

 bore fruit. As there was no staniinate tree ot the species in Berlin, Gled- 

 itsch ordered pollen sent from I^eipzig. The journey required nine days, 

 and although Gleditsch thought the pollen spoiled, the male inflorescence 

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

 germinated in the following 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 the 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 morphologist and of the experimenter 

 liave 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 

 veiy prevalent in the 18th century, and Kaspar Friedrich Wolf (1759) has 



