33 



As Camerariiis first i)i'oved the sexuality of plants, and Koelreuter 

 showed that dlflerent species can unite sexually to produc(! hybrids, so 

 Spreiigel demonstrated that a certain ^cind of liybridization was very com- 

 mon in the vegetable kingdom, namely the crossing of flowers of different 

 individuals of the same species. To him belongs the credit for having first 

 shown the part played by insects in cross pollenatiou, and pointing out the 

 correlation between such properties of the flower as color, odor, nectar, 

 special forms and markings, and so forth, and the visiting insects. 



Karl Friederick Gaertner, son of Joseph Gaertner, took up the work so 

 ably begun by Koelreuter, and greatly extended the knowledge of hybridi- 

 zation, having kept accurate account of nine thousand experiments. His 

 work was published in 1849. Sachs states that "These observations once 

 more confirmed the existence of the sexuality in plants, and in such a 

 manner that it could never again be disputed. When facts were observed 

 in ISGO, which led to the presumption that under certain circumstances in 

 certain individuals of some species of plants, the female organs miglit pro- 

 duce embryos capable of development without the help of the male, there 

 was no thought of using these cases of supposed parthenogenesis to dis- 

 prove the existence of sexuality as the general rule ; men were concerned 

 only to verify first of all the occurrence of the phenomena, and then to 

 see how they were to be reasonably understood side by side with the ex- 

 isting ideas of sexuality." Gaertner's experiments were conducted at 

 Claw, in Wurtemberg, the place in which Koelreuter carried on his studies ; 

 Camerarius worked in Tubingen. 



While the experimenters in hybridization were at work, the student 

 with the microscope was no less busy. In 1823, Amici discovered the pollen 

 tube in the stigma, and the fact was confirmed by others. In 1830, the 

 same observer traced the pollen tube into the ovule. Schleideu and 

 Schacht now came forward with their erroneous theory of the formation 

 of the embyro in the seed. They maintained that the embyro develops 

 from the end of the pollen tube after the latter enters the ovule. It is 

 clear that this doctrine would do away with the essential point in the 

 sexuality of plants, for the ovule would be regarded merely as an incu- 

 bator for the embyro. Amici, in 184G, brought forth decisive proof for the 

 view he had maijitained. namely, that the embryo arises not from the end 

 of the pollen tube, but from a portion of the ovule which already existed 

 btfore fertilization, and that tliis part is fertilized by a fluid contained in 



[3—181921 



