viii GENERAL KEY TO THE ORDERS. 



** Embryo normally with 2 cotyledons; stems differentiated into pith, 

 wood and bark ; leaves mostly net-veined. Subclass 2. DICOTYLEDONES. 306 



f PETALS DISTINCT TO THE BASE, OR WANTING (the two lower petals more 

 or less united in family Papilionaceae; two inner petals or all four of them 

 coherent in family Fumariaceae ; three petals united with each other in family 

 Polygalaceae ; five petals sometimes slightly united in Oxalis, and in the 

 family Ilicaceae). Series I. Choripetalae. 306 



J Petals none (except in family Portulacaceae and in most Caryophyl- 

 laceae, which are herbs with the leaves nearly always opposite, the seeds with 

 endosperm, and in the pistillate flowers of the walnuts) (Juglans). 



Calyx none (except in the family Juglandaceae, trees with odd-pinnate leaves). 

 Marsh herbs with small perfect flowers, in nodding spikes in our species. 



Order 2. PIPERALES ^307 



Trees or shrubs ; staminate flowers, and sometimes also the pistillate, in aments. 

 Leaves simple. 



Fruit many-seeded ; seeds with a tuft of hairs at one end. 



Order 3. SALICALES 307 



Fruit i-seeded. 



Stigmas 2 ; ovule orthotropous ; endosperm none 



Order 4. MYRICALES 320 



Style stigmatic above ; ovule amphitropous ; endosperm thin. 



Order 5. LEITNERIALES 321 



Leaves odd-pinnate ; fruit a nut enclosed in a husk. 



Order 7. JUGLANDALES 322 



Calyx present. 



Flowers, at least the staminate ones, in aments. Order 8. FAGALES 326 



Flowers not in aments (in ament-like spikes in Morus) ; but variously clustered, 

 or rarely solitary. 



Flowers monoecious, dioecious or polygamous (sometimes perfect in Ulmus) \ 



ovary superior, i-celled. Order 9. URTiCALES 337 



Flowers dioecious or perfect ; ovary inferior, at least in part. 



Ovary i-celled. Order n. SANTAL,>I.ES 344 



Ovary several-celled (usually 6-celled flowers perfect). 



Order 12. ARISTOLOCHIALES. 346 



Flowers mostly perfect in our genera (dioecious in some species of Rumex 

 in the family Polygonaceae ; monoecious or dioecious in some Chenopo- 

 diaceae and Amaranthaceae) ; ovary superior. 



Embryo straight or nearly so ; fruit an achene. 



Order 13. POLYGONALES 350 



Embryo coiled, curved or annular ; fruit not an achene. 



Order 14. CHENOPODIALES . . 367 



|| Petals present (wanting in Ceratophyllaceae, aquatic herbs with whorled 

 dissected leaves; in many Ranunculaceae; in Cafycocarpum, a dioecious vine 

 of the Menispermaceae; in Lauraceae. alternate-leaved aromatic trees and 

 shrubs; in Podostemaceae, aquatic herbs with the simple flowers involucrate; 

 in LiqWrdambar, a tree of the Hamamelidaceae with palmately lobed leaves 

 and capitate flowers; in Sanguisorba, pinnate-leaved herbs of the Rosaceae; in 

 Xanthoxylum, pinnate-leaved trees of the Rutaceae; in Euphorbiaceae; in 

 Callitrichaceae, Empetraceae and Buxaceae; in some of the Aceraceae and 

 Rhamnaceae; in Thymeleaceae, Elaeagnaceae and in some species of Lud- 

 wigia in Onagraceae; in Hippuris and Proserpinaca of the Haloragidaceae, 

 and in Nyssa of the Cornaceae). 



A. Ovary superior, free from the calyx (partly or wholly inferior in some Saxifra- 

 gaceae, in Hydrangeaceae, Grossulariaceae, Hamamelidaceae, Pomaceae, and 

 Loasaceae). 



Carpels solitary, or several and distinct (united in some Nymphaeaceae) : sta- 

 mens mostly hypogynous and more numerous than the sepals; sepals mostly 



distinct. Order 15. RANALES 405 



Carpels 2 or more, united into a compound ovary; stamens hypogynous; sepals 

 mostly distinct. 



Plants not insectivorous. Order 16. PAPAVERALES. . . 437 



