FERTILITY IN CICHORIUM INTYBUS 
the self-pollination of different sister plants is quite as fluctuating in 
degree as is the production of seed itself. In its effect it is often quite 
like the conditions observed in the "zygotic sterility" which Davis 
(1915a, 1915&, 1916) has observed in the Oenotheras, especially those 
of hybrid origin. In chicory, however, the noticeable failure in seed 
production suggests that much of the embryo abortion observed may 
also involve a sort of sexual incompatibility. Embryo abortion, how- 
ever, may be due purely to conditions of nutrition, especially in those 
species which exhibit no physiological incompatibility. 
The incompatibilities in chicory are obviously not purely a question 
of haploid against diploid, but of a particular kind of haploid and 
diploid relationship. In discussing these various points, the writer 
( 1 916, p. 436-440) has pointed out that our knowledge of the physiology 
of pollen-tubes is scarcely sufficient to decide whether the critical 
point in the growth of the pollen-tube is determined by purely nu- 
tritive reactions with the pistil as such or whether it is really deter- 
mined by the diffusion of secretions (hormones) from the macro- 
gametophyte. The writer hopes to be able to state later somewhat 
definitely from cytological investigation what the relative develop- 
ments and nuclear phenomena in chicory are. 
In discussing the various aspects of the relation of cell organization 
to the development of compatibilities and incompatibilities, the writer 
(1916, p. 416) has pointed out that the role of any particular combina- 
tion of germ plasm elements, as far as can be judged by their expression 
as characters in parents, in sister plants and in offspring, must be 
quite secondary as far as incompatibilities are concerned to a more 
general quality of the tissue and cell organization that develops in 
connection with ontogenetic growth and development. The con- 
ceptions of Jost (1907), Morgan (1904, 1910), and East (191 5) are 
fundamentally based on this same generalization as I there pointed out. 
Much the same idea, if I understand their position aright, has since 
been expressed by Goodspeed and Clausen in stating that such cases 
of physiological incompatibility seem to involve "non-specific" dis- 
turbances in the "reaction systems" (germ plasm) (1917a, p. 46). 
These authors have embodied in the conception of "reaction systems" 
(1916, 1917a) a view which in some measure is a revolt against the 
extreme formalism of the Mendelian factorial hypothesis, and in this 
sense the conception is useful in the interpretation of the phenomena 
of sterility especially of the type I have called impotence. In their 
