THE FLOWER 



91 



The Primitive Flower 



The type of flower now generally recognized as morphologically 

 simple is one that shows the least change, under adaptive evolutionary 

 modification, from the original primitive flower. Evidence now seems to 

 support strongly the theory that the ancestral flower was bisexual, with 

 numerous stamens and carpels, without a perianth, or with a uniseriate 

 perianth of simple, bractlike organs. (This theory differs greatly from 

 that still held by some botanists that the primitive flower was uni- 

 sexual.) All the appendages were spirally arranged, and the flower was 

 symmetrical and without fusion among its parts. From this theoretically 

 basic flower— essentially the "pattern flower" of preevolutionaiy tax- 

 onomy — have developed many lines of modification, with reduction 

 producing types more simple in kinds and number of organs, and with 

 elaboration producing complexity in form. 



The major principles of evolutionary modification, upon wliich is 

 based the acceptance of this type of flower as morphologically simple 

 and primitive among living forms, are the following advances: 



1. From many parts, indefinite in number, to few, definite in number 



2. From three or four sets of appendages — perianth, androecium, and 

 gynoecium — to one 



3. From spiral to whorled arrangement of appendages 



4. From freedom of floral parts to fusion — connation and adnation 



5. From radial symmetry ( actinomorphy ) to bilateral symmetry 

 ( zygomorphy ) 



In these principles, there is important departure from those of the 

 Engler system of classification, which has long formed the foundation 

 of the natural system of plant classification and is still largely in use in 

 herbaria. The major difference lies in the interpretation of simplicity. 

 Under the Engler system, the primitive flower is unisexual; advance is 

 seen to bisexual flowers and to increase in number of sporophylls. In 

 more recent classifications, fewer kinds and smaller number of ap- 

 pendages represent specialization — reduction by loss of parts. This 

 viewpoint has brought major changes in phylogenetic relationships 

 of both large and small taxa; taxa formerly believed primitive are now 

 considered advanced, and new lines of apparent relationship have been 

 drawn. Prominent among these changes is the interpretation of the 

 unisexual flower with few sporophylls as advanced, rather than primi- 

 tive. 



Reduction in the Flower 



Reduction in the flower may occur in many or all parts, simul- 

 taneously in several parts, or progressively from part to part. Loss may 



