FERTILITY IN CICHORIUM INTYBUS 
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 very 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, 1 916). 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. 
