BIOTYPES AND HYBRIDS. 49 



0688. Most of these plants produced fruit, and in all cases this was flat 

 and triangular to obcordate, like that of B. burs a-pas torts . Unguarded 

 seeds of 3 of these and guarded seeds of 1 were used for the production of 

 second-generation families, 1 as 0689.196 and 3 collected together as 

 0689.197. The descriptions of the second-generation families follow : 



0689.196 : Seeds of this plant, which had been carefully guarded against 

 cross-pollination, were sown October 12, 1906, and 217 plants were raised, 

 of which 188 lived to produce seed. These had the following composition: 

 98 were B. bursa-pastoris heteris, 36 B. dp. tennis, 32 B. bp. rhomboidea, 13 

 B. bp. simplex, 5 B. heegeri heteris, 1 B . h. tennis, 2 B. h. rhomboidea, and 

 1 B. h. simplex, giving, so far as the rosette -characters are concerned, a 

 very close agreement with the ratio 9:3:3:1, but in the form of capsule 

 showing a very great preponderance of the btirsa-pas torts type. 



0689.197: Seeds of 3 unguarded sibs of the parent of the last family 

 were sown October 15, 1906, under this number. Of 2,014 offspring, 1,815 

 came to maturity, and were recorded as having the following composition : 

 1,032 were B. bursa-pastoris heteris, 331 B. bp. tennis, 302 B. bp. rhomboidea, 

 78 B. bp. simplex, 45 B. heegeri heteris, 13 B. h. temiis, 13 B. h. rhomboidea, 

 and 1 B. h. simplex (plates 3 and 4). Again there is a close agreement in 

 the leaf-characters with the typical dihybrid ratio, 9:3:3:1, and a notable 

 deficiency in the occurrence of the heegeri type of capsule. 



0688.212 : Seeds of this unguarded plant, which was a reciprocal of the 

 parents of the last two families described, were sown October 12, 1906, and 

 produced a large progeny, of which 621 unselected plants were potted for 

 study and the rest discarded. Of these 621 plants, 537 reached maturity 

 and were classified thus : 317 B. bursa-pastoris heteris, 102 B. bp. tennis, 

 67 B. bp. rhomboidea, 21 B. bp. simplex, 19 B. heegeri heteris, 7 B. h. tennis, 

 and 4 B. h. rhomboidea, noB. h. stmp/exbeing observed. The same general 

 relations of the rosette-characters and capsule-characters are obvious here 

 as appeared in the other two F 2 families described, but there is not quite 

 as close agreement with the ratio 9 : 3 : 3 : 1 as in the other families, prob- 

 ably because this family became somewhat diseased and the distinguishing 

 of the several types of rosette became consequently more difficult. 



Reviewing the results of crossing- Bursa bursa-pastoris simplex and B. 

 heegeri, it is seen that the Fj hybrids are essentially uniform, no matter in 

 which direction the cross is made, and that the rosette in either case is of 

 the heteris-rhomboidea type, owing- to the incomplete dominance of heteris, 

 while the capsule is always of the bursa-pastoris type. In F 2 there appear 

 the 4 types of rosette already described, in combination with each type 

 of capsule. The rosette presented many instances of the best- developed 

 examples of the 4 described forms, particularly interesting being the fact 



