6 BOTANICAL GAZETTE [july 



^ 



mutation or in the first hybrid generation^ but apparently arises only 

 from self-fertilized hybrids of the second or later hybrid generations. 



In these crosses it should be said that^ while constancy of the 

 forms appearing in the F, is the rule, exceptionally in one of the types 

 which ordinarily breeds true an individual may appear whose progeny 

 repeat the two types of the grandparents, thus showing a tendency to 

 continue splitting (DeVries /. c. 2:423), 



Shull's^ recent work on hybridization in the elementary species 

 of Bursa (Capsella) shows that these produce ordinary Mendelian 

 hybrids in no way comparable to Oenothera hybrids. In fact I think 

 it is safe to say that no genus of plants or animals is known in which 

 the conditions of hybridization are strictly comparable to those found 

 in Oenothera. This peculiar type of hybridization is not confined 

 to O. Lamarckiana and its mutants, but ordinarily appears when a 

 mutant is crossed with another member of the genus, as O, muricata^ 

 O, biennis^ O. hirtella^ O. suaveolens^ O. hirsutissima. In such cases 

 the first hybrid generation usually contains both the parent forms in 



" " w 



widely varj^ing proportions, and these in the F^ are found to breed 

 *'"ue. Thus the same type of hybrid is produced as is usual when a 

 mutant is crossed with O. Lamarckiana: 



The phenomena of hybridization in Hieracium are more nearly 

 like those of Oenothera than any other genus, so far as I know. 

 Mendel's^ original work, continued recently by Ostenfeld,' has 

 given us a view of the hybridization conditions in this genus. Men- 

 del showed in a number of Hieracium crosses that the F^ is hetero- 

 geneous, including some intermediate types and some ver}^ near to or 

 indistinguishable from the parents. In the case of H. praealiumX 

 H. flagellarCy the F^ obtained by self-pollinating the hybrids of the 

 Fi was shown to be the same as the F^, all the forms of the latter 



5 S HULL, G. H., Elementary species and hybrids in Bursa. Science 25:590- 

 591. 1907. 



^ Mendel, G., Uebereinige aus kiinstlicher Befruchtung gewachsene Hieracium- 

 Bastarde. Verb. Naturf.-Vereins. Briinn. 8:26-31 (Abhandlungen). 1869. 



7 OsTENFELD, C. H., Castration and hybridization In the genus Hieracium. Rep. 

 3d Intemat. Conf. on Genetics. Jour. Roy. Hort. Soc. London 24:285-288. 1900. 



— , Experimental and cytological studies in the Hieracia. I. Castration and ' 



hybridization experiments with some species of Hieracia. Bot. Tidssk. 27:225-248, 

 pi, I. 1906. 



