172 Plant Life and Evolution 



envelope, if present at all, is of the simplest char- 

 acter (Fig. 1 8, A, B). 



The petaloideous forms show great variety, and 

 it is not easy to reduce them all to one series. 

 The type of the flower found in the buttercup or 

 magnolia is regarded as primitive, but it is difficult 

 to connect these forms with such apetalous flowers 

 as those of the poplar or oak, for example. There 

 are other simple petaloideous types, such, for exam- 

 ple, as the pinks, portulacas, etc., which are quite 

 different from such apocarpous types as the butter- 

 cup or water-lily. These lower petaloideous types 

 have been called Choripetalse, and have the petals 

 entirely separate. The number of carpels and 

 stamens may be quite indefinite or they may be of 

 definite number. 



The specialization of the flower in the dicotyle- 

 dons has proceeded very much in the same way 

 as among the monocotyledons, and affords an- 

 other example of parallel development. There is 

 first an indefinite number of entirely separate parts, 

 then a reduction in the number of stamens and 

 carpels, and a tendency toward a coherence of cer- 

 tain parts, resulting in a more or less tubular flower, 

 with inferior ovary and a reduced number of sta- 

 mens. Where the petals are grown together the 

 flower is said to be " sympetalous," and the Sym- 

 petalae, which include all such flowers, are consid- 

 ered by botanists to be the most highly specialized 

 of the dicotyledons (Fig. 18, E; Fig. 19, F). 



