72 CENTAUREA AMERICANA. AMERICAN CENTAUKEA, 



growth of a stem of a composite is made up of a spiral of five 

 leaves ; as these over-lap in the growth-coil the outer edge of 

 each leaf makes a light ridge. There are, therefore, five distinct 

 ribs in many composite stems, and which when the stem is cut 

 across so often give it a five-angled appearance. As the spiral 

 has not been drawn out in forming the head as in the stem 

 orrowth, the united bases of the leaves cannot take on the five- 

 angled plan, but are numerously arranged around a common 

 centre, and afford us some idea of their great number by the 

 little ridees we see. 



Explanations of the Plate. — i. Opening flower. 2. Nearly mature flower, showing the 

 involucral scales. 3. Floret with young achene at the base. 4. Scale from the inner part 

 of the flower. 5. Scale from the exterior. 



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