Minnesota Plant Life. 



improved. Especially in the 

 composite family should it 

 be observed that the ftower 

 cluster has become an area 

 perfected under somewhat 

 the same laws that were seen 

 to govern the perfecting of 

 the flower. It will be re- 

 membered that the flower 

 itself is supposed to have 

 originated from groups of 

 leaves arranged on a slender 

 axis. As this axis aban- 

 doned itsstarchmaking 

 work, the leaves were gath- 

 ered into a more compact 

 structure by the shortening 

 of their general stem. Thus FlG ' m - Water bur - mari s old - After Britton 



and Brown. 



from cones like those of the 



pines arose the flatter aggregates of spore-bearing leaves known 

 as "flowers" in the higher plants. These flowers were essentially 



branches of the stem and in 

 the lower families such 

 branches more commonly 

 maintained their primitive po- 

 sition with reference to each 

 other, so that the flowers were 

 arranged loosely upon the 

 plant. In higher forms defi- 

 nite flower clusters of particu- 

 lar shape came into existence 

 and the law of condensation 

 finally permitted the produc- 

 tion of the flat-topped cluster 

 of the sunflower in which hun- 

 dreds of flowers are gathered 

 together on a broad circular 

 disk. Among these flowers of 



FIG. 210. Corn-flower. After Britton and 



Brown. the disk a division of labor 



