SELF FERTILIZATION 319 



As to the causes of these differences between transplantation and fertiliza- 

 tion, we may consider the following facts : Correns as well as East, in their 

 analysis of self-sterility, compared the results of various combinations, some 

 of which correspond to a syngenesious, others to a homoiogenous relation- 

 ship. They observed the behavior of sperm and tgg, or of pollen-tube and 

 style, toward each other in individuals closely related, as well as in those not 

 closely related though belonging to the same species. In the case of fertiliza- 

 tion, the individuals belonging to the same family could be arranged in a few 

 groups in such a way that all the members of the same group behaved in an 

 identical manner, whereas in the case of transplantation various gradations 

 could be found in syngenesious reactions, ranging from those seen in autog- 

 enous, to those seen in homoiogenous transplantations. 



There remains still to be considered a third difference between transplanta- 

 tion and fertilization. While after autotransplantation antagonistic reactions 

 between host and transplant in higher organisms are lacking, in syngenesio- 

 transplantation they occur sooner or later if sensitive tissues are used. On 

 the other hand, in some experiments in plants fertilization between members 

 of the same group (syngenesious fertilization) and self-fertilization were 

 equally unsuccessful, while fertilization between individuals belonging to 

 different groups did succeed. However, a condition corresponding to what 

 we find in auto- and syngenesiotransplantation in mammalian tissues, has 

 been observed by Correns also in the case of fertilization in a plant, namely, 

 in Tolemiea Menziesii. Here, individuals of the F x generation can be readily 

 fertilized by one another, as well as with both parents, whereas self- 

 fertilization is impossible. This may be considered as another type of self- 

 sterility and it corresponds to what we find in transplantation if we choose, 

 for instance, the thyroid gland as a test object, and the presence or absence of 

 a reaction as the standard for measurement. In transplantation as well as in 

 the case of fertilization in Tolemiea, it appears that a greater number of factors 

 is required than in the other instances of pollination, mentioned above, in order 

 to explain the results in accordance with the rules of Mendelian heredity. 



In hetero-pollination, including pollination between different varieties as 

 well as between different species, there may develop disharmonies of various 

 kinds, which may be similar to those observed in attempted self-fertilization. 

 Thus, lack of germination of the pollen-grain and inhibition in the down- 

 growth of the pollen-tube into the style may be noted in both cases; like- 

 wise, in hetero-pollination there may be in addition an interference with 

 those mechanisms which direct the movement of the pollen-tube through the 

 micropyle toward the ovulum. It seems, therefore, that the specific chemo- 

 tropically active substances, which function under these conditions, are not 

 interacting in a normal manner with the pollen-tube. The relationship between 

 substances of this kind and the pollen-tube is evidently a specific one, which 

 is graded in accordance with the genetic relationship between the interacting 

 organisms, and these substances behave, therefore, in this respect, in a manner 

 similar to the organismal differentials of the tissues in higher organisms. 



But if hetero-fertilization should actually take place, leading to the produc- 



