FLOWER CHART xv 



pound ovary with the petals elevated upon it. The petals themselves 

 show no change in the direction of union in the families between the roses 

 and the honeysuckles, this step of advance being apparent first only in 

 the latter group and in the bluebells. As in the other two lines of de- 

 velopment, the final change in the buttercup-aster line affects the shape 

 of the corolla. The change often appears in different form, however, for 

 instead of specializing the shape of each separate flower, the aster group 

 is characterized by the collecting together of the separate flowers into a 

 close head of flowers, and only the outer row or rows of these possess 

 an irregular corolla. In the aster or daisy, what seems to the casual ob- 

 server a single large star-like flower is in reality a whole cluster of flowers. 

 Certain ones of these, i. e. the yellow ones in the center, are specialized 

 for seed-production while those on the outer edge, which are commonly but 

 wrongly called "petals," are set apart for insect-attraction by means of 

 their long, ribbon-like corollas. Not only are the asters, or composites, 

 considered the mostly highly developed group in the plant kingdom, be- 

 cause of the fact that they have taken the four steps of advance, but also 

 because of this community arrangement of the single flowers, the speciali- 

 zation of the different flowers to different tasks, and the consequent greater 

 efficiency of the group in the matter of seed-production. 



Use of the Chart as a Key to Orders 



In using the chart as a key for determining the group to which a flower 

 belongs, it is absolutely essential for satisfactory results that the structure 

 of the flower in question be correctly determined. This is recorded in the 

 form of the flower-formula. The next point is to note what steps of ad- 

 vance this structure indicates and hence which of the three lines is to be 

 followed. Having once determined the proper line of development, this 

 should be followed just as far as the steps of advance indicate, as shown 

 by the cross lines, taking these strictly in order. If there are several 

 groups in the region thus finally arrived at, the flower in question should 

 be assigned to the one which it most closely resembles in structure as 

 indicated by the flower-formula. The practical working out of the above 

 rules may best be shown by taking a few flowers and "running them down" 

 in this way. A knowledge of the meaning f such terms as "petals," 

 "sepals," "corolla," "calyx," "pistils," "ovary," "compound ovary" and "sta- 

 mens" is absolutely essential to the use of even the simplest key to flower- 

 ing plants. These are all defined in the glossary, but are most readily recog- 

 nizable from the color plates. 



A knowledge of how to express flower structure in the symbols of a 

 flower-formula is also essential. In this, the symbols are as follows : Ca— 



