xvi INTRODUCTION 



calyx ; Co corolla ; S stamens ; P pistils ; Sc scales. The pappus or 

 calyx of the aster family is written Ca p . The number immediately follow- 

 ing the symbol in each case denotes the number of sepals in the calyx, of 

 petals in the corolla, of stamens in the flower, simple pistils or of cells in 

 a compound one, etc. Union of any part is indicated by a ( ) around the 

 figure denoting the number of parts. Elevation of the petals and sepals 

 on the ovary, as well as the attachment of stamens to the tube of the 

 corolla in those flowers with united petals, is shown by a horizontal line 

 below the parts elevated. Irregularity of the corolla is indicated by sepa- 

 rating the petals into groups, i. e. the characteristically 2-lipped corolla of 

 the mints and snapdragons, in which there are 2 petals in one lip and 3 

 in the other, is written Co (3+2) . The corolla of the pea, which consists 

 of 2 wings, 2 petals united into the keel, and the standard, is written 

 Co 2+2+1 ; the characteristic lip-like petal of the orchids is indicated as Co 2+1 . 



In order of importance in determining flower relationship and hence 

 classification, the step of advance which affects the pistil comes first, i. e., union 

 of simple pistils into a compound one ; and the elevation of the corolla on the 

 ovary, second. The other two changes affect the corolla also, and of these 

 the uniting of the petals into a bell or tube is of most importance, while 

 the change in shape is of the least weight in determining flower relation- 

 ships. This is because irregularity of corolla, though characteristic of all 

 the highest groups, may occur occasionally in almost any group, even the 

 buttercups. For this reason, the steps of advance must be followed in the 

 order in which they occur, across any of the three lines of development, 

 and no one can be "skipped" in order to reach a farther one. This will 

 become clear in the examples given below. Since the ovary is the key- 

 note to the family relationships, one must be very careful to determine 

 with certainty whether it is simple or compound, and if the latter, exactly 

 how many cells it possesses. This must be done by a cross-section of as 

 mature an ovary as possible, and determined not from one specimen alone 

 but from several. It is well to study the other parts from several speci- 

 mens also, as variations from the normal may occur in any one and so 

 spoil results. 



Let us now take a flower with 5 sepals, 5 petals, 10 stamens and a 

 compound pistil with 5 cells. The formula for this would be Ca 5 Co 5 S 10 P (5) , 

 and the steps of advance thus indicated would be only that of a united 

 pistil. Now, looking at the chart, one sees two directions in which one 

 may follow up a line possessing united pistils, the left-hand one and the 

 right-hand one. But, the former comprises only those flowers with a num- 

 ber-plan of 3, while the right-hand line is composed of 4 and 5-plans. 

 This starts us along the buttercup-mint line. Since the flower in question 



