CHROMOSOME NUMBERS IN THE GENUS BURSA. 



415 



It is planned to continue this work next year when more ma- 

 terial is available, completing the counts for the species of the 

 Bursa-pastoris group, and examining a certain number of the 

 inter-group hybrids. I had at first planned to study the details of 

 the maturation mitoses, but the small size of the chromosomes and 

 the difficulty of securing satisfactory material in the right stages 

 of division make it unlikely that this will be attempted. 



FIG. i. 



FIG. 2. 



FIG. I. Anaphase of first maturation division of B. grandiflora. X 3,ooo. 

 FIG. 2. Metaphase of first maturation division of B. occidcntalis. X 3,ooo. 



Figures are given for B. grandiflora and B. occidcntalis only, 

 but in the later paper figures will be given for all of the species 

 counted. 



LITERATURE CITED. 

 Laibach, F. 



'07 Zur Frage nach der Individualitat der Chromosomen im Pflan- 



zenreich. Beih. Bot. Centralbl., 22:191-209. 8 figs. 

 Marchal, E. 



'20 Recherches sur les variations numeriques des chromosomes dans 

 la serie vegetal. Mem. de 1'Acad. Roy. de Belgique (Cl. des 

 Sci.), 4: i-ioS. 4 pis. 

 Rosenberg, O. 



'04 Ueber die Individualitat der Chromosomen im Pflanzenreich. 



Flora, 93: 251-259. 7 text figs. 

 Shull, G. H. 



'26 Species Hybridizations among Old and New Species of Shep- 

 herd's Purse. Proceedings International Congress of Plant 

 Sciences (4th International Botanical Congress), Ithaca, 1926. 



