Trees of New York State 37 



pression, or union of parts that is quite beyond belief. Botanists 

 observed this long ago and have learned from experience that 

 the variation in the flower best indicates the natural affinities 

 of flowering plants. Plants with comparable floral structures are 

 related to each other. Flowers may be classified according to 

 these variations as follows: 



A. Suppression and symmetry of parts. 



a. Perfect. With stamens and pistils (essential organs) 



present. 



b. Imperfect, With stamens or pistils or both in sepa- 



rate flowers. 



1. Monoecious. With the staminate and pistillate 



flowers on the same plant. 



2. Dioecious. With the staminate and pistillate 



flowers on separate plants. 



3. Polygamous. With the perfect and imperfect 



flowers on the same plant. 



(a) Polygamo-monoecious. With the perfect 



and both sorts of imperfect flowers on 

 the same plant. 



(b) Polygamo-dioecious. With perfect and 



staminate flowers on one plant and per- 

 fect and pistillate on another. 



c. Complete. With all four sets of floral organs present. 



d. Incomplete. With one or more sets of floral organs 



lacking. 



e. Regular. With the individuals of each set similar in 



form and size. 



f. Irregular. With the individuals of some sets vary- 



ing in form or size from the others. 



B. Position of parts. 



a. With reference to insertion on the receptacle. 



1. Spiral. With floral organs spirally arranged. 



2. Cyclic. With the parts of each set all inserted 



on the receptacle at the same height. 



b. With reference to each other. 



1. Flower hypogynous. With the three outer 

 (lower) sets inserted below^ the ovary. 

 (a) Strictly hypogynous. With the three outer 

 (lower) sets inserted separatel}' below 

 the ovary. (Fig. 47.)' 



