FERTILITY IN CICHORIUM INTYBUS 389 



generation of crosses between the wild plant A and plants of the cul- 

 tivated common chicory {E Series) are somewhat higher than those 

 of the Fi generation (RA plants) derived by crossing this same wild 

 plant with plants of the red-leaved Treviso here reported. The 

 strain (E) has not, however, been inbred in pedigreed cultures as has 

 the red-leaved Treviso strain, so there are less adequate data on the 

 comparative value of inbreeding and. crossing with this variety. 



The character of physiological self-compatibility giving fertility 

 appears in a \ery irregular and sporadic manner, and it exists in dif- 

 ferent degrees of intensity in different plants. It has appeared in 

 chicory in a family of the variety known as red-leaved Treviso after 

 three generations of self-sterile ancestry and no doubt would occur 

 with equal irregularity and intensity after many generations of such 

 ancestry. It seems very conclusive therefore that the causes of self- 

 incompatibilities are not to be ascribed to a similarity of nuclear 

 constitution involving definite hereditary units of germ plasm which 

 either directly determine incompatibilities (especially Correns's view 

 of line-stuffs) or which indirectly determine them (East's view). 

 Furthermore, the variability of the offspring grown from self-fertile 

 plants in chicory shows a very irregular inheritance of the. characteristic 

 of self-compatibility and makes it quite clear that the expression of 

 self-compatibility is quite of the nature of a fluctuating variability, 

 and that self-compatibility and self-incompatibility, in chicory at 

 least, are not to be described in terms of dominant and recessive 

 characters which behave in any sort of Mendelian manner. 



The evidence seems conclusive that the actual .conditions giving 

 the various grades of self-compatibility, and of self-incompatibility 

 (undoubtedly there are various grades of incompatibility giving com- 

 plete sterility) as well, are decidedly individual. Various aspects of 

 this question in relation to conceptions of fertilization and to the 

 phenomena of serum incompatibilities have already been discussed 

 (Stout, 1916). It must be remembered that a plant whose two sets 

 of sex-organs are completely incompatible is itself derived from the 

 fusion of two cells that were compatible. The interactions between 

 pistil and pollen-tubes were compatible. The germ plasms of the 

 two sex cells were compatible in fusion, in the somatic life of the 

 diploid cell structure of the resulting individual, and in the more 

 intricate interactions involved in sporogenesis occurring in that indi- 

 vidual. Yet in cases of complete self-incompatibility none of the 

 pollen grains are functional on the pistil of the plant. 



