DKOTTLEDONE8. 473 



when dried and powdered constitute the ginger of commerce. That 

 from the West Indies, called Jamaica Ginger, is considered the best. 



Sub-Order Canute, with one polliniferous stamen, bearing a 

 one-celled anther. Aside from Camia, with its many ornamental spe- 

 cies now common in gardens, one other plant deserves mention, viz. : 



Maranta arundinacea, a native of tropical America, now grown ex- 

 tensively for its fleshy rhizomes, from which a starch known as "Arrow- 

 root " is obtained. 



566. Cohort XV. Hydrales. Small aquatic plants, with 

 a hexamerous regular perianth, and stamens three, six, nine, 

 or twelve. 



Order Hydrocharideee. This contains the Eel Grass, Vcdlisneria 

 spiralis, and Water Weed, Anacharis Ganadenis, 

 common in our ponds ; the latter is naturalized in 

 England, where it chokes up streams. 



Fossil Monocotyledons. The earliest Mono- 

 cotyledon, so far as known at present, was a Tri- 

 assic species of Yuccites, doubtfully referred to the 

 Liliaceae. In the Jurassic the Gramineae, Cyper- 

 aceae, Liliaceae, Naiadaceae, and Pandanaceae were Fig see. Diazram 

 represented by a few species. In the Cretaceous the of ihe flower of C'an- 

 T . . * , na, showing theoreti- 



Caunae, Dioscoreaceai, and PalUMCeee appeared. cai structure. After 



A species of the last-named order has been discov- Sacl18 - 

 ered in the Cretaceous of Western Kansas. In the Tertiary most of the 

 modern orders of Monocotyledons were represented (however, no orders 

 of Cohorts II., III., and XIII. have yet been found). Fifteen species 

 of palms have been described from the Tertiary of the Great Plains 

 and the Rocky Mountain region,* extending as far north as northern 

 Dakota and Vancouver's Island. Their remains are also abundant in 

 the Tertiary of Mississippi. 



SUB-CLASS DICOTYLEDONES. 



(Exogence of De Candolle.f) 



567. In the plants of this sub-class the first leaves of the 

 embryo are two and opposite, hence they are said to have 

 two cotyledons. The venation of the leaves is for the most 



* " Contributions to the Fossil Flora of the Western Territories. 

 Part II. The Tertiary Flora," by Leo Lesquereux. Washington, 1878. 



f From the Greek lu, outside, and yeveiv, to bring forth. The 

 name is no longer a proper one, as we now know that these plants 

 are not, strictly speaking, " outside growers ; " on the contrary, they 

 increase in thickness by the growth of an internal meristem layer. 



