stout: pollinations in cichorium intybus 403 



2. The conception that the causes of this type of steriHty are 

 purely individual and due solely to the fact that the two kinds of 

 sex organs are produced by a single individual irrespective of any 

 particular type of inherited nuclear or cell organization. Jost's 

 conception of individual chemical stuffs that are similar in the sex 

 organs of an hermaphrodite individual, and Morgan's view of 

 similarity in so-called protoplasmic association inhibiting gametic 

 union respectively. These conceptions emphasize internal en- 

 vironment. 



3. The view that this sort of sterility is due to too great a simi- 

 larity of nuclear constitution as regards certain definite hereditary 

 units, (a) In a similarity involving the presence in the gametes 

 of an hereditary unit solely associated with the production of a 

 so-called line stuff: emphasis is placed on a particular germ plasm 

 constitution; the view held by Correns, Baur, and Compton. 

 (b) In the relative similarity of the male gametophyte only (in 

 respect to any one or more hereditary units of any sort) to the 

 hereditary complex of the sporophyte; East's view. 



These divergent views are, for the most part, due to the par- 

 ticular emphasis which the one or the other investigator has given 

 to certain phases of the phenomenon or to certain facts obtained in 

 their particular experiments. They all agree in making similarity 

 or lack of differentiation in sex organs responsible for the incom- 

 patibility. 



Darwin considered that the constitution of sex elements may, 

 to a considerable degree, be influenced directly by changed condi- 

 tions of growth (theory of pangenesis). The persistent self- 

 sterility of strains of plants like Eschscholtzia he considers a direct 

 but rather incidental influence of external environment which 

 reduces the sex differentiation that usually gives fertility. He 

 attempted to distinguish this sort of influence from that which he 

 thought operates through inbreeding in which the degree of rela- 

 tionship, as he believed, also influences the degree of compatibility 

 of the sex elements. The cases of a markedly decreased fertility 

 seen in cross-bred but self-sterile plants did not agree with Darwin's 

 view that crossing increases fertility, hence Darwin rather unduly 

 emphasized the fluctuating and sporadic nature of such sterility, 

 ascribing its causes also to change in environment. 



My plants of chicory are grown under as nearly uniform con- 



