42 BURSA BURSA-PASTORIS AND BURSA HEEGERI : 



characters of B. bp. tennis without exception in 330 individuals. In the 

 offspring" of 3 heterozygous plants that have been tested, the ratios 2.44 : 1, 

 2.5 : 1, 3.23 : 1, and 3.44 : 1 have appeared, and these are no doubt as 

 near 3 : 1 as the smallness of the families should have led us to expect. 



056.130: Besides these 2 original hybrid families, it will be recalled that 

 certain unexpected individuals of B '. bp. rhomboidca in one of the original 

 families of B. bp. simplex (056) were supposed to be due to chance crosses 

 (see p. 26). Seeds of one of these (056.130) were sown June 6, 1906, and 

 produced 217 B. bp. rhomboidca and 72 B. bp. simplex, that is, in the ratio of 

 3.01 : 1, thus showing' the assumption that they were of hj r brid origin to 

 be correct. (See plate 2). 



In addition to the hybrids brought in from nature and their self-fertilized 

 offspring as represented by the 31 families which are described above, 7 

 first-generation hybrid families between different biotypes of Bursa bursa- 

 pastoris have been produced by artificial crossing. Only one F 2 family has 

 been reared from these to the present time. 



0515.93 : The mother of this cross was a specimen belonging to the 

 second original family of B. bp. hctcris (0515) described above (see p. 14). 

 This plant was castrated and pollinated with pollen from a specimen of the 

 first original culture of B. bp. tennis (0519, see p. 22). The seeds were 

 sown May 2, 1906, and produced 222 plants, all resembling the mother and 

 possessing the essential features of B. bp. heteris. 



0693.203 : Self-fertilized seeds of 3 guarded specimens belonging to the 

 last-described family were sown together October 12, 1906, and gave a 

 progeny of 111 specimens, 84 of which were typical B. bp. heteris and 27 

 B. bp. tennis, or in the ratio 3.1 : 1. (See plate 1.) 



As no other artificially-produced hybrids between biotypes of B. bursa- 

 pastoris have been studied beyond the first generation and only facts bear- 

 ing upon the question of dominance can be derived from these cultures as 

 yet, it seems best to postpone their discussion until the second generation 

 has been studied. This is the more important, since the specimens chosen 

 for crossing in a number of instances belonged to families whose relations 

 to the 4 biotypes which have been involved in the above-described natural 

 hybrids are still in doubt. 



The occurrence of supposed hybrids among the biotypes of Bursa bursa- 

 pastoris has been noted by Almquist (1907, pp. 22 and 88-89), who also 

 refers to descriptions of similar cases by Von Borbas and by Grenier. The 

 actual hybrid character of the plants mentioned is very doubtful, however. 

 The assumption of their hybridity is based wholly upon the facts of inter- 

 mediacy and sterility, together with the vegetative vigor and longevity 

 which are certainly correlated with sterility. I have occasionally observed 

 such sterile or nearly sterile plants in progenies produced from seeds fully 



