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THE AMERICAN NATURALIST [Vol. XLV 



not universal, among the forms of the species. The 

 lower portions of the stigma lobes in the hud lie below the 

 tips of the anthers which discharge their pollen before 

 the bud opens. As a result the stigma is not only well 

 pollinated in the bud, but cytologieal studies on my 

 strains A and B have shown that the pollen tubes reach 

 the embryo sacs before there is any opportunity for cross 

 pollination. Hybridization in nature could hardly occur 

 in these forms unless their own pollen should be insuffi- 

 cient for the number of ovules in the ovary or was much 

 slower than foreign pollen in effecting fertilization; al- 

 ternatives that are very unlikely. These conditions, 



are present in all of the forms of biennis known to the 

 writer, and have been noted bv De Vries for the Euro- 

 pean types. As a result a strain once established is cer- 

 tain to remain pure throughout at least the great mass 

 of its seeds. 



The chief characteristics of the biennis strains A and 



