148 



the experiments described below, indicate that there are two 

 groups of evening primroses in the eastern United States : (i) 0. 

 biennis, 0. iiiuricata, 0. Onkcsiana and 0. cniciata, with compara- 

 tively small flowers, in which self-pollination is possible and fre- 

 quent ; (2) 0. argillicola, 0. grandijlora, and O. Laviarckiatia of 

 a southern range and with flowers large and accessory structures 

 favorable to cross -pollination. 



The experimental work consisted in growing Ocnotlicra biennis 

 in order to observe the changes produced by cultivation. Care- 

 ful measurements of the plants were made, and it was further 

 established that 0. biennis is capable of self-fertilization by rea- 

 son of the superior length of the stamens. A new wild species, 

 0. argillicola Mackenzie, was tested and its distinctive characters 

 demonstrated. 0. cruciata (Nutt.) Small, also, was grown in the 

 experimental grounds, and the evidence at hand seems to confirm 

 the suggestion as to the mutability of the species. It was, there- 

 fore, found important by the experimenters, aided by the critical 

 descriptive study of the experimental plants by Miss A. M. Vail 

 and Dr. J. K. Small, to give the characters of the forms of this 

 species secured. Professor MacDougal has also been careful to 

 hybridize 0. LajnarcJdana and 0. cruciata, as well as 0. Lainarck- 

 iana and O. biennis, 0. Lanmrckiana and O. nutricata, in order 

 to determine by this analysis the relationships between O. Lain- 

 arckiana and other species of the genus. It was shown that the 

 hybrid progeny in the cultures, made in the New York Botan- 

 ical Garden and in Amsterdam, included a series of types which 

 ranged, in the aggregate of characters included, from those rep- 

 resenting pure strains of both parents through goneoclinic forms 

 to intermediates in which parental characters were, more or less, 

 equally apparent. The experiments show also that the hybrid 

 0. Laviarckiana X O. biennis includes four distinct and separate 

 forms, none of which is identical with the unilateral monotypic 

 hybrid obtained in the same cross in Amsterdam. Attention 

 was paid to the occurrence of mutants among the hybrids, and 

 with a description of these the first part of the paper closes. 



The .second part of the publication is a statistical comparison 

 of Oenothera Laviarckiana with two of its mutants by Dr. G. H. 



