216 
IOWA ACADEMY OF SCIENCES. 
Fig. 9. Leaves of the thistie ( Cnicus odoratus). 
like Cnicus arvensis , 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 examined 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. 
f.Ludwig. Lehrbuch der Biologie der Pflanzen 489. 
"Anton Kerner von Marilaun. Pflanzenleben, Si. 
C. M. Weed. Ten New England Blossoms and Their Insect Visitors. 126. 
L. H. Pammel. Flower Ecology . 71. 
Herman Muller. Fertilization of Flowers, Eng. Trans , Thompson. 340. 
Charles Robertson. Flowers and Insects. Rosaceae and Composite. Trans. Acad. Sci.. 
St. Louis, 6:475. 
Halsted, B. D. : Observation Upon the Common Thistle. 
Rep. Dept, of Bot. Ia. Agrl. Coll 1886:29. 
