31 



Oayuga region. 



Another Introduced weed that can stand little com- 

 petitlon, hut thrives on rich cultiyated land in spite 

 of all ordinary attempts at suppression* Like Brassioa 

 arrensis , it strongly contrasts with Barharea -mlgaris 

 in its restricted range of habitat. No attempt has been 

 madOy naturally, to collect specimens illustrative of 

 the distribution; the main aim has been to illustrate 

 the variation in leaf -form. Several experimenters have 

 shown by pedigree cultures the existence of various 

 genetic types in this species; the writer simply illus- 

 trates this variability* for the most part* by a few 

 series of specimens each taken from a single small area 

 on one day. 

 Diagnosis: 



Recognizable at once by the flat* triangular pods. 

 Variation : 



Sheet 27 (one specimen) shows a very small plant* 

 with leaves almost absolutely entire* that very closely 

 resembles the var. nana of F. B« and E. S. Clements 

 (Herbaria Formationum Coloradensium) * as shown in the 

 general herbarium of Cornell University. 



The leaf -form of a given individual may change " 

 greatly with the season and the age of the plant (see 



