414 



Minnesota Plant Life. 



improved. Especially in the^ 

 composite family should ii 

 be observed that the flower 

 cluster has become an area 

 perfected under somewhat 

 the same laws that were seen 

 to govern the perfecting of 

 the Hozvcr. 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 its s t a r c h m a k i n g 

 work, the leaves were gath- 

 ered into a more compact 

 structure by the shortening 



of their general stem. Thus ^'''- ■'^- water bur-mangoUl. 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 

 .>/ / y/j^ branches more commonly 

 1^^^ maintained their primitive po- 

 -isition 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. thc (lisk a (livisiou of labor 



