BURSA BURSA-PASTORIS AND BURSA HEEGERI 3 



demonstrated their distinctness and permanence beyond a possible 

 question. These four types are distinguished from each other by 

 characteristic lobation of the leaves. For convenience I have as- 

 signed to these four forms the names Bursa bursa-pastoris heteris, B. 

 bp. rhomboidea, B. bp. tennis, and B. bp. simplex. It has been impos- 

 sible to determine which of Almquist's elementary forms agree with 

 these, but it is almost certain that each of these four forms is more in- 

 clusive than his described forms, and that under each of these headings 

 should be grouped several of his named elementary species. These 

 four types may be briefly characterized as follows : 



Type (a). Bursa bp. heteris has the leaves divided to the mid- 

 rib, the terminal lobe being usually separated from the nearest lateral 

 lobes by clean, deep incisions. The lateral lobes consist essentially 

 of two features, an elongated proximal portion, the "primary lobe/' 

 and a more or less rounded or angular portion, the "secondary lobe, 

 in the distal axil of the primary lobe." Several of Almquist's re- 

 cently described elementary species obviously fall under this head, 

 his B. bp. angustiloba representing the most pronounced type, and 

 Wittrockii, rubella, and others doubtless belong here. From the de- 

 scriptions and photographs I have been unable to determine which 

 is the first of his elementary species which should be classed here. 

 This is an important matter because it would determine the priority 

 of names. 



Type (b). Bursa bp. rhomboidea has the leaves divided to the 

 midrib as in type (a). The lateral lobes have an incision on the distal 

 margin setting off the rounded secondary lobe from an unelongated 

 primary lobe, the secondary lobe corresponding with the rounded 

 distal component of the heteris lobe. There is usually a corresponding 

 incision on the proximal margin of the primary lobe. In the best 

 developed specimens these incisions set off a small terminal portion 

 which is rather blunt or angular at the apex, being generally of rhom- 

 boidal form. Less perfectly developed specimens have the incisions 

 very shallow, or nearly wanting. Here may belong Almquist's B. bp. 

 polyedra, densa, and alpina. 



Type (c). Bursa bp. tennis'. This differs from both (a) and (b) 

 in that the sinuses do not usually reach the midrib and the terminal 

 lobe is not set off from the nearest lateral lobe by a clean-cut incision 

 reaching almost or quite to the midrib. The lobes are more or less 

 elongated and sharp, entirely lacking the rounded secondary lobe. 



Type (d). Bursa bp. simplex. Like the last, this form is scarcely 

 ever divided nearly to the midrib, and the lobes are mostly obtuse, 

 sometimes more or less acutish, but never long and attenuated. 



I have studied over twenty families of hybrids, among these four 

 elementary species, and find that they represent the four terms of a 

 typical Mendelian dihybrid, the alternate characteristic being, Aa, 

 an elongated primary lobe vs. no elongated primary; and, Bb, a 



