216 



IOWA ACADEMY OF SCIENCES. 



Fig. 9. l^ea\es oi the thistie {C'>!uus odoratus). 



like Cnicus arcensis, are perennial, and propagate by under- 

 ground rhizomes, this being the chief mode of propagation 

 for the Canada thistles in the west.* 



* Although this species seeds abundantly in the east, seed is seldom produced in the west. 

 Though many hundreds of plants have been e.xamined by the writer west of Lake Michigan, 

 in but a few instances have seed been found. A few were once found near Lincoln Park, and 

 in abundance near Milwaukee, and once in northeastern Iowa. Experiments made as to their 

 germination proved that the seed found in Milwaukee germinated freely. 

 t.Ludwig. Lehrbuch der Biologie der Pflanzen 489. 

 "Anton Kerner von Marilaun. Pflanzenleben, 5S. 



C. M. Weed. Ten New England Blossoms and Their Insect Visitors. 126. 

 L. H. Pammel. Flower Ecology . 71. 



Herman MuUer. Fertilization of Flowers, Eng. Trans , Thompson. 340. 

 Charles Robertson. Flowers and Insects. Rosacea? and Composite. Trans. Acad. Sci.. 

 St. Louis, 6: 475. 



Halsted, B. D. : Observation Upon the Common Thistle. 

 Rep. Dept. of Bot. la. Agrl. Coll 1S»6: 29. 



