DICOTTLEDONE8. 473 



when dried and powdered constitute the ginger of commerce. That 

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



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

 one-celled anther. Aside from Canna, with its niauy ornamental spe- 

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



Maranta arundinocea, 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, Vallisneria 

 spiralin, and Water Weed, Anacharis Canadensis, 

 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 Yuccifes, doubtfully referred to the 

 Liliaceae. In the Jurassic the Gramineae, Cyper- 

 aceae, Liliaceae, Naiadaceae, and Paudanaceae were -p\s. 366 Diagram 



represented by a lew species. In the Cretaceous the of l ^e flower of Can- 

 ,, Tx . , na, showing tneoreti- 



tauua?, Dioscoreaceie, and Palmaceai appeared. cai structure. After 



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

 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 betn 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 

 *,he Tertiary of Mississippi. 



SUB-CLASS II. BICOTYLEDONES. 



(Exogeim 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 t-fw, outside, and -yfveiv, 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. 



