159 



The production of a considerable number of hybrid families 

 representing the various possible combinations of these four 

 t>iotypes has demonstrated that their gametic formulae may be aptly 

 represented by the conventional Mendelian symbols, as follows : 



B. bp. heteris . . AB 



B. bp, rliomboiäea . aB 



B. bp. tenuis . . Ab 



B. bp. Simplex . . ab 



By comparing these formulae with the descriptions of the differ- 

 ent forms it will be seen that A is responsible for the long, 

 sharp character of the primary lobe in B. bp. heteris, and the 

 attenuation of the lobes in B. bp. tenuis, while B produces the 

 division of the leaf to the mid-rib and the resultant definiteness 

 of the terminal lobe in both B. bp. heteris and B. bp. rliomboiäea, 

 the rounded secondary lobe of B. bp. heteris, and the proximal 

 and distal incisions of B. bp. rliomboiäea. 



Bursa Heegeri has the heteris-fovm of rosette, i. e. with the 

 gametic formula AB, but differs so fundamentally from Bursa 

 bursa-pastoris in the characters of the capsules, that if its rela- 

 tionship to the latter species were not so obyious on other 

 grounds, its capsules would cause it to be placed unquestionably 

 in a separate genus. The flat, triangulär or cordate form of the 

 bursa-pastoris capsule is too familiär to need description. The 

 spur-like valves are firm, and fall readily at the slightest touch 

 when the seeds are ripe. The capsules of B. Heegeri are of oval 

 form, surmounted by the short, strong, persistent style, and the 

 yalves are thin membranous, not the least inflated, and do not 

 fall when the seeds are mature. The seeds are liberated by an 

 irregulär break in the central region of each valve. 



When this original genotype of B. Heegeri was crossed 

 reciprocally with B. bursa-pastoris simplex, the rosette-characters 

 segregated in the F 2 , into the four types described above, but 

 the Heepen- type of capsule appeared in only 111 specimens 

 among 2540. The distribution of the several characters in the 

 3? 2 are shown in the following table : 



