404 PLANT MORPHOLOGY 



Umbellales. The Umbellales constitute the highest order of the Archi- 

 chlamydeae. They include 3 famihes and about 3,000 species, nearly all 

 herbaceous. Of these, 2,500 species belong to the Umbelliferae, where 

 are found such familiar forms as carrot (Daucus), celery (Apium), pars- 

 nip (Pastinaca) , and dill (Anethum). The order is characterized by reg- 

 ular, epigynous flowers having a tetramerous or pentamerous perianth, a 

 reduced calyx, a single whorl of stamens, and usually a bicarpellary, biloc- 

 ular ovary with a single ovule in each locule. The floral formula of the 

 Umbelliferae, 5-5-5-2, is an advanced one. 



2. Metachlamydeae 



The Metachlamydeae are characterized chiefly by their sympetalous 

 corollas, and so are often called the Sympetalae. The entire group has 

 reached a condition of definite numbers for all the floral sets, and therefore 

 is constantly cyclic. The stamens are generally attached to the corolla. 



Ericales. The Ericales comprise about 2,000 species of woody plants, 

 mostly shrubs. Of its 6 families, the Ericaceae, with about 1,500 species, 

 is by far the largest. It includes such well-known genera as azalea 

 (Rhododendron), wintergreen {Gaultheria), heather (Calluna), heath 

 (Erica), and blueberry (Vaccinium). The flowers of the Ericales are 

 regular or nearly so, tetramerous or pentamerous, pentacyclic or some- 

 times tetracyclic, mostly isocarpic, hypogynous or often epigynous, and 

 syncarpous. In tetracyclic flowers the stamens are opposite the petals. 

 The ovary is multilocular. Some of the Ericaceae are choripetalous and 

 in nearly all the stamens are free from the corolla. Thus this order serves 

 to connect the Archichlamydeae and Metachlamydeae. 



Primulales. The Primulales constitute an order of about 1,100 species 

 of herbs grouped into 4 families, of which the Primulaceae is of chief 

 interest. The representative genus is primrose (Primula). The flowers 

 are regular, pentamerous, tetracyclic, isocarpic, mostly hypogynous, and 

 syncarpous. The single whorl of stamens stands opposite the petals and 

 not, as in the higher tetracyclic orders, alternate with them. The outer 

 whorl of stamens is often vestigial. The ovary is unilocular and has 

 free-central placentation. In some respects this order resembles the 

 Centrospermales. 



Ebenales. This is an order of about 1,000 species of tropical trees and 

 shrubs. There are 4 small families, the characteristic one being the 

 Ebenaceae, of which the ebony and persimmon (Diospyros) are examples. 

 The flowers are regular, tetramerous or pentamerous, pentacyclic, iso- 

 carpic, mostly hypogynous, and syncarpous. The ovary is multilocular. 

 The floral parts show some variation in number, with an occasional 

 increase in stamens and carpels. 



The preceding orders constitute the pentacyclic isocarpic series of 



