DICOTYLEDONS 



213 



less completely united, and the corolla is " sympetalous," 

 or " gamopetalous." The greater number of these, in 

 addition to their being more highly specialized, indicate 

 that they are, as a 

 whole, a later and 

 more differentiated 

 group than the Cho- 

 ripetalae, although it 

 must be remembered 

 that certain families 

 of the latter are 

 highly specialized. 

 The highest of the 

 Sympetalae, how- 

 ever, are probably 

 the most recent and 

 highly developed of 

 all plants. 



The Sympetalae 

 fall readily into two 

 main divisions, the 

 Isocarpae, which 

 have the carpels 

 equal in number to 

 the petals, and the 



Anisocarpae, in which they are fewer. None of the Sym- 

 petalae ever have the carpels separate, but they are 

 always completely united into a compound pistil. The 

 Isocarpae are supposed to be the more primitive of the 

 two divisions, and a few of them have the petals almost 

 free (Fig. 52, C), and to some extent connect the Cho- 

 ripetalae and Sympetalae. Of these isocarpous forms the 



rz? 



FIG. 52 (Sympetalre). A, flower of wild 

 Azalea (A. viscosa),one of the isocarpous 

 Sympetalae : all the parts of the flower in 

 fives ; B, a section of the ovary of Azalea, 

 showing the five divisions ; C, flower of 

 the pine-sap (Monotropa), the petals and 

 sepals quite separate ; D, flower of the 

 sorrel-tree (Oxydendrum), the petals co- 

 herent almost to the tips ; E, flower of 

 shooting-star (Dodecatheon), one of the 

 primrose family : F, flower of Petunia, 

 one of the anisooarpous Sympetalae ; 

 parts of the flower in fives, except the 

 two carpels, shown in the cross-section 

 of the ovary, G. 



