72 DISEASE IN PLANTS 



again by Tulasne, De Bary, Strasburger and 

 others ; but Pfeffer brought the matter to a crisis 

 by discovering the attractive (chemotactic) sub- 

 stance emitted in given cases, and by collecting 

 the fertilising bodies by its means into artificial 

 tubes. 



The fusion of the nucleated bodies in the sexual 

 act was observed by Strasburger in the living 

 plant a few years ago, and numerous later observers 

 have confirmed it. Meanwhile all the stages of 

 approach and contact of the essential filaments of 

 the nuclear substance have been traced, as also 

 all the stages of the transference of half of each 

 filament, male and female, into each of the first 

 two cells of the very young embryo-plant. 



Moreover, the essentials are found to be the 

 same in the animal kingdom also, and the bearing 

 of all these discoveries on the phenomena of 

 reproduction, variation, and heredity in living 

 organisms has been and is of the highest import- 

 ance, for they support, control, explain and correct 

 so many ofthe splendid results of Knight, Kolreuter, 

 Sprengel, Hildebrand and Hermann Mtiller, and in 

 every direction throw side-lights into the crevices 

 of that magnificent structure, the theory of Natural 

 Selection, erected for all time by our countryman, 

 Charles Darwin. 



To return now to experiments on crossing. It 

 is found that the first products of the crossing 

 appear exactly alike ; they may have characters 

 intermediate between those of the father and 

 mother, or they may resemble one more than the 



