280 MORPHOLOGY 



16, 17. (9 families, 2760 species.) These families are clearly special 

 branches from Ranales, the most specialized one probably being the 

 mustards (Cruciferae). 



18. Rosales (16 families, 14,270 species). This is the greatest 

 alliance among the Archichlamydeae, including far the largest family 

 the Leguminosae, with over 11,000 species. Another prominent 

 family is the Rosaceae, which gives name to the alliance. These two 

 families are plainly branches from the Ranales; and among the Legu- 

 minosae the flowers become conspicuously irregular. The irregularity 

 is of a special type, illustrated by the sweet pea, so that a large part of 

 the family is easily recognized. In the development of irregularity in 

 connection with insect pollination, the Leguminosae hold the same 

 position among Archichlamydeae that the orchids (Orchidaceae) hold 

 among monocotyledons. 



19-25. (99 families, 27,358 species.) This is a tangle of seven 

 alliances leading off in every direction from the preceding ones, each 

 alliance characterized by some special feature. Each one, however, 

 gradually becomes more definitely cyclic and approaches the epigynous 

 condition. 



26. Umbellales (3 families, 2660 species). This is easily the highest 

 of the alliances of Archichlamydeae and it is kept from being included 

 among the higher Sympetalae only because it is polypetalous. The 

 dominant family is the parsley family (Umbelliferae), and associated 

 with it are the dogwoods (Cornaceae). The floral formula is definitely 

 as follows: sepals 5, petals 5, stamens 5, carpels 2, and this is also the 

 most advanced floral formula found among Sympetalae. Associated 

 with this high formula is epigyny. Another high character is that the 

 flowers are small and massed, the cluster being more or less invested 

 by a rosette of bracts (involucre). Apparently as a result of the 

 massing of the flowers, the sepals are much reduced, and the whole 

 cluster shows more or less division of labor, some flowers (the peri- 

 pheral ones) often being more showy, and the others more fertile. 



SYMPETALAE 



This is a much better defined group than the Archichlamydeae, from 

 which they are certainly derived. The combination of characters is 

 as follows : completely cyclic flower, sympetalous corolla, ovule with 

 a single massive integument, and complete absence of wall tissue in 

 the ovule (see p. 263). About 42,000 species and 51 families are recog- 



