214 



DIOSCOREACE^. 



[DlCTYOGENS, 



Order LXVIII. DIOSCOREACE^.— Yams. 



Lioscorese, R. Brown Prodr. 294. (1810) ; Ayardh Aphor. 169. (1823) ; Ach. Rich. Nuuv. Elem. 434. 

 (1828/ ; Endl. Gen. Ivii.— Dioscoreaceae, Ed. Pr. cclvii. ; Meisner, p. 404. 



Diagnosis. — Dictyogcns with unisexual jiowers, an adherent perianth, and consolidated 



several-seeded carpels. 



Twining shrubs, with lai-ge tubers either above or below ground. Leaves alternate, 



occasionally opposite, with reticulated veins. Flowers small, spiked, vAi\\ from 1 to 3 



bracts each, J $ . Calyx and corolla confoimded, herbaceous, adherent. $ Stamens 



6, inserted mto the base of the sepals and petals ; 

 anthers tm'ned inwards, bm'sting longitudinally. 

 9 Ovary adlierent, 3-celled,with 1- or 2-seeded cells ; 

 style deeply trifid ; stigmas undi^^ded ; ovules sus- 

 pended, anatropal. Finiit leafy, compressed, with 

 two of its cells sometimes abortive ; occasionally 

 succulent. Seeds two in each cell, or by abortion 

 soUtary, compressed, ^^•inged or wingless, or in the 

 succulent species roimdish ; embryo small, near 

 the hilum, l^ing in a large cavity of cai'tUagiuous 

 albumen. 



According to Brown this Order is separable from 

 SarsapariUas by the tlireefold character of inferior 

 ovary, capsular fruit, and albumen having a large 

 cavity. Tamus is, however, between the two Orders, 

 agreeing with SarsapariUas in its baccate, with 

 Yams in its inferior fruit. — Prodr. 294. EndUcher 

 says it has no obsciu'e resemblance to Bh'thworts, 

 and it is probably in this place that that singxilar 

 Order finds one of its nearest relationships ; in 

 fact, the woody tissue of the common Yam aiTanges 

 itself in the stem very much in the same manner as 

 the wedges of Aristolochia. 



Although the genera are few m number the spe- 

 cies are numerous, and are found exclusively in tro- 

 pical coimtries of either hemisphere, if Tamus be 

 excluded, wliich is a native of Eui'ope and the tem- 

 perate parts of Asia. 



An acrid principle exists in the plants of this Or- 

 der, and when concentrated renders them danger- 

 ous. Tamus commmiis, for example, has a lai'ge 

 fleshy root, so acrid as to have been formerly em- 

 ployed for stimulatmg plaisters, whUe the tubers of 

 Dioscorea triphylla and dsemona have dreadfully 

 nauseous qualities even after being carefully cooked. 

 Nevertheless, this principle is more generally so 

 much diffused as to be of no importance : hence the 

 principal part of the species belonging to the genus 

 Dioscorea produce what are called Yams, large, 

 fleshy, farmaceous tubers, which form as important 

 an article of food in tropical comitries as the Potato in Em-ope. The young suckers of 

 Tamus communis (the afi-rreXos fMcAuLva of Dioscorides, and o^pva of the modern Greeks,) 

 and also of T. cretica, are eaten in Greece like Asparagus, as we learn from Sibthorp ; 

 but Endlicher says, that unless they are well boiled (dihgentius coquantiir) they are 

 powerfully pm-gative, and even emetic. 



Fig CXLV. 



Tamus, L. 



Tamnus, Juss. 

 Testudinaria, Salish. 



GENERA. 

 Rajania, L. I Dioscorea, L. 



Janraja, Plum. Ubium, Rumph. 



Oncus, Lour. 

 Podianthus, Schnitzl. 



Numbers. Gen. 6. Sp. 110. 



Position. Dioscoreace^. — Smilaceae. 



Aristoloc?iiacece. 



Fig, CXLV.— Dioscorea adenocarpa; l. a section of its male flower; 2. a seed vessel open ; 3. a seed. 



