GENTIANALES. 503 



Species of NemopMla, Pliaeelia, Whitlama, etc., are cultivated in 

 flower gardens. 



Order PolemoniaceaB. — Mostly herbs of North America and North- 

 ern Asia, numbering about 150 species. 



Species of Phlox, Gilia, Polemonium, Cdbcea, etc., are cultivated in 

 flower gardens. 



583.— Cohort XV. Gentianales. Plants with opposite 

 leaves, regular flowers, superior ovary, and the stamens usu- 

 ally as many as the corolla lobes and alternate with them. 



Order Grentianaceee. — The Gentian Family. Annual or perennial 

 herbs, with a watery juice ; ovary generally one-celled, with many 

 ovules. The species, of which there are about 500, are found mostly 

 in temperate and cold climates. Tliey possess a bitter principle, which 

 has been employed in medicine. We have many very pretty wild 

 species. 



Order Ijoganiaceee. — Woody plants almost entirely of the tropics, 

 with two-celled ovaries. About 350 species are known ; they contain 

 -a bitter principle which is often exceedingly poisonous. 



Strychnos nux-vomiea is a small tree of India, bearing an orange-like 

 fruit containing numerous large iiattish seeds (3 cm. in diameter). 

 These seeds constitute the poisonous drug, Nux Vomica ; they con- 

 tain two alkaloids to which their activity is due, viz , Strychnia 

 (Cji H22 N2 O2) and Brucia (C23 H^b N2 O4 -f 4 Hs 0). The ordinary 

 form of the first as found in the shops is a Sulphate of Strychnia. 



S. toxifera, a tree of the northern parts of South America, yields 

 from its bark and young wood the famous poison known as Curare, 

 Urari, Ourari, Woorara, etc. 



iS. Tieute, a Javanese climber, furnishes the virulent Upas TieutS 

 or Tjettek with which the natives poison their arrows. 



Order Asclepiadacese. — The Milkweed Family. Woody or herba- 

 ceous plants, with a milky juice ; ovaries two, distinct, but with a 

 ■single common stigma; pollen agglutinated into masses (poUinia). 

 This large order of about 1300 species is chiefly tropical, being abun- 

 dantly represented in America, Africa, and Asia. The milky juice con- 

 tains Caoutchouc, and usually acrid and poisonous principles. But few 

 of the species are of sufficient economic importance to demand notice. 

 Many have a local reputation as domestic medicines. (Figs. 428-33.) 



Some are favorites in the flower garden or conservatory, e.g., the Wax 

 Plant of India (Hoya carnosa), species of Oeropegia, Stephanotis, Peri- 

 ploca, etc. The South African Stapelias resemble Cacti, being fleshy 

 and leafless ■ 



The peculiar structure of the flowers in this order has recently been 

 shown to be for the purpose of securing the services of insects in the 

 -process of pollination. 



