194 



THE AMERICAN NATURALIST [Vol. XLVIII 



account of certain cultures of Capsella, in which muta- 

 tions were simulated, would be of timely interest. 



During the winter of 1908-1909, I collected in a green- 

 house at Ann Arbor, Michigan, and at the disposal of the 

 Botanical Department of the University of Michigan, 

 twelve rosets of Capsella Bursa- past oris, the leaves of 

 which showed certain more or less striking morphological 

 differences. With the hope of isolating certain biotypes, 

 the rosets were placed in pots and permitted to flower. 

 No measures were taken to prevent the accidental trans- 

 ference of pollen, but the pots were placed about six 

 inches apart. This, as will be shown later, is the only 

 precaution necessary to guard against cross-pollination, 

 provided the cultures are carried on in a greenhouse and 

 during the winter months. After a portion of the seed 

 had ripened, the plants, the majority of which retained 

 their climax leaves, became herbarium specimens. More 

 recently, after constant association has enabled me to 

 detect minute differences, it has been possible to identify 

 some of these plants witli two of the biotypes described 

 by Shull, 7 to wit, rlunuhnuh-a and simplex. At the time 

 of collection, the differences were sensed, but could not be 

 described technically, since the extent of the influence 

 wielded by fluctuating variability was an unknown quan- 

 tity. Never before had I so fully realized the truth of de 

 Vries's statement. 8 



We are trained to the appreciation of the differentiating marks of 



The seed obtained was sown in sterilized soil during 

 the spring of 1910. From each seedpan 60 individuals 

 were transplanted to flats. As the plants grew older, it 

 was found that, with a single exception, the seedlings in 

 each of the flats were uniform, but that the seedlings in 

 the different flats were not alike, three types being dis- 

 tinguishable. The interest in these types, for the isola- 



* Shull, G. H., "Bursa bursa-pastoris and Bursa Heegeri: Biotypes and 

 Hybrids," Putt. No. 112. Carnegie Institution of Washington, 1909. 

 s de Vries, Hugo, ' ' Species and Varieties, ' ' 689, 1905. 



