44 BURSA BURSA-PASTORIS AND BURSA HEEGERI : 



here the likelihood of a new origin is certainly exceeded by the probability 

 that a seed was carried to this spot by some agency from a nearby culture, 

 for it had been grown for several years at Dahlem in an unprotected bed 

 several hundred meters from the place in which Laubert discovered it. 

 Hus (1908) takes the alternative view, however, and considers this a case 

 of repeated mutation.* Laubert points out that in addition to the capsule 

 character noted by Solms-Laubach, there are other characters of the stem 

 and inflorescence which serve to distinguish B. heegeri from its supposed 

 parent and which would suggest a more distant relationship with that form 

 than had been supposed; but, on the other hand, he found that in both 

 species there occur frequent instances of abnormal pistillate but sterile 

 flowers in the lower portion of the flower- stem, and he takes this fact, 

 together with the occurrence of capsules occasionally simulating those of 

 B. bursa-pastoris, formed when B. heegeri is attacked by Albugo and Pero- 

 nospora, as additional proofs that B. heegeri is a derivative from B. bursa- 

 pastoris. Of the manner of its origination from B. bursa-pastoris nothing 

 is known, of course, but Potonie (1906) suggests that it is a reversion 

 induced by some pathological condition. 



More recently Noll (1907) has investigated some plants resembling B. 

 heegeri, which had already been found by Melsheimer in 1882 in htmdreds 

 in a field of Dattenberger Flur and again in 1884 on a height at Linz. Mels- 

 heimert considered these plants hybrids, but could not suggest the prob- 

 able parents, while Kornicke and Wirtgent stated that they are doubtless 

 identical with Bursa heegeri. Specimens of Melsheimer 's plants were 

 placed in Petry's herbarium bearing the label "Capsella bursa-pastoris 

 forma caps, ovatis. ' ' Noll received this material from Petry, together with 

 living specimens collected by the latter at Didenhofen, Metz, Hagendin- 

 gen, and Kreuznach. A careful comparison of the anatomical features of 

 these plants with those of Bursa heegeri and B. bursa-pastoris led Noll 

 to the conclusion that the Melsheimer plants are not Bursa heegeri, but 

 a sterile form of B. bursa-pastoris, to which he gives the name Capsella 

 pseudo-heegeri. The finding of these plants in considerable numbers tends 

 to weaken the argument that the discovery of B. heegeri in a region so well 

 known proves it to be a recent mutation. Perhaps Bursa heegeri will yet 

 be discovered in some abundance in some locality where it has hitherto 

 escaped notice. 



*I have called the attention of Dr. Hus to this matter and he concedes in a letter 

 that my explanation of the occurrence of B. heegeri in nature at Dahlem is probably the 

 correct one. 



t Mentioned by Noll, but not verified by me. 



