22 BURS A BURSA-PASTORTS AND BURS A HEEGERI : 



The two specimens (040.19 and 040.26) which form the basis of all my 

 pure-bred cultures of this biotype, germinated in vessels of earth over 

 which were unpacked Bursa seed which had been sent by Prof. H. F. Rob- 

 erts, of Manhattan, Kansas, and as the soil of one of these vessels had been 

 sterilized it seems almost certain that these plants came, from seed sent 

 from Kansas. Seeds of these two plants were sown September 22, 1905, 

 and January 31, 1906, and tog-ether gave a progfeny of 361, all but 4 of 

 which were referable without question to the type of the parents. These 

 4 specimens in family 0519 which were not quite in agreement with the rest 

 had the lobes comparatively broad and short, though still strongly acute, 

 and the margins were slightly crenulate or denticulate (fig. 11). As these 

 specimens were somewhat stunted, it is thought that their differences may 

 have been due to the causes producing the stunting, but this point has not 

 yet been tested. 



Besides these two pure -bred families of B. bp. tenuis coming presumably 

 from Manhattan, Kansas, this form appeared as a component of a hybrid 

 family received from Edgewood, New Carlisle, Ohio, and also as a mem- 

 ber of a hybrid family from Chicago, Illinois. These hybrid families will 

 be discussed later. 



Bursa bursa-pastoris rhomboidea n. sp. element. 



This, like B. bp, heteris, has the leaves divided to the midrib and pos- 

 sesses a similar, more or less rhombic terminal lobe, set off by deep sinuses 

 from the nearest lateral lobes. Each lateral lobe of the climax-leaves 

 usually shows a prominent incision on its distal margin, by which a lobe 

 is formed next to the rachis, corresponding to the secondary lobe of B. bp. 

 heteris, and in well-developed specimens there are usually one or two sim- 

 ilar incisions on the proximal margin. All lobes formed by these incisions 

 are usually obtuse or broadly angular. The terminal portion of the lateral 

 lobes has in the best-marked examples a nearly rhombic form, which sug- 

 gested the name (see figs. 18 and 20, and plates 2 and 4). When grown 

 under unfavorable conditions the characteristic incisions may be lost, the 

 prominent incisions setting off the rounded secondary lobe being the most 

 persistent. Almquist's C. bp. subalpina (his fig. 46) , dens a (fig. 51) , polyedra 

 (fig. 52), and perhaps two or three others may belong here. 



Three pure cultures demonstrated to belong to B. bp. rhomboidea have 

 been reared from specimens or seeds brought in from nature, and the same 

 elementary species has been included as hybrids in two other original 

 families. Complete proof of its elementary character will appear below in 

 the section on hybrids. 



Cultures derived from two plants growing side by side near the Brooklyn 

 Institute's Marine Biological Laboratory at Cold Spring Harbor, Long 

 Island, were thought for a time to belong to a biotype distinct from the 



