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THE AM ERIC AX XA TURA LEST [Vol. XXXV 1 1 . 



iacere, families in which the flowers are zygomorphous and often 

 of large size. It has been suggested that these two divisions 

 represent two distinct lines of development and are of very 

 different origin. The Composite are derived through the 

 Rubiacex and Caprifoliacerc from the Umbelliferae, while the 

 aroids are assigned as the remote ancestors of the labiate forms. 

 It seems better, however, to regard the series as homogeneous. 

 The gamopetalous families probably had a common starting 

 point and are derived from a group of primitiv e tonus allied to 

 the progenitors of the Choripetalai, but a later offshoot, and still 

 retaining affinities with the monocotyledons. The flowers are 

 characterized by denniteness in the number of parts and by their 

 frequent cohesion, characters, says Engler, which must have 

 become fixed at a very early period in their history. The Gamo- 

 petalas are of later occurrence in the fossil state than the 



