BICOTTLEDONES. 



473 



■when dried and powdered constitute the ginger of commerce. That 

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



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

 one-celled anther. Aside from Ganna, 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 Hydrocharidese. — This contains the Eel Grass, ValUsneria 

 spiralis, 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 Tuceites, doubtfully referred to the 

 Liliacese. In the Jurassic the Graminese, Cyper- 

 acese, Liliaceae, Naiadacese, and Pandanaceae were yig age.— Diagram 

 represented by a lew species. In the Cretaceous the of the flower of "Can- 

 ^ ^ ,^. , „ , J raa, showing thcoreti- 



Caunae, Dioscoreaceai, and Falmacea; appeared. cai structure. — After 



A species of the last-named order lias been disco v- Sachs. 

 €red in the Cretaceous of Western Kansus. 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 

 +,he Tertiary of Mississippi. 



Sub-Class II. Dicottledones. 



{ExogencB of De Candolle.f) 



567. — In the plants of this sub-elass 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 i^u, outside, and yeveiv, to bring forth. Tke 

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

 are not, strictly speaking, " outside gi'owers ; " on the contrary, they 

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



