IN EXTRA-TROPICAL COUNTRIES. 277 



dried drug are obtained from a single plant several years old. 

 An important orange-red crystalline substance, emodin, allied 

 to chrysophanic acid, occurs in genuine Rhubarb. A large 

 proportion of the medicinal Rhubarb-root is now grown in 

 England. 



Rheum officinale, Baillon.* 



Western China and Eastern Thibet on the high table-land. 

 It furnishes the most of the true Turkey Rhubarb, not merely 

 from the root, but also from the woody stem. Suited for 

 mountainous regions. Recommended also as a scenic plant 

 by Regel. 



Rheum palmatum, Linne.* 



From insular to Alpine North-Eastern Asia. A variety from 

 the Tangut country of Mongolia or North Thibet yields an 

 excellent medicinal root known as the Kiakhta or Khansu 

 Rhubarb (Maximowicz) ; valuable also as a decorative plant. 



Rheum Rhaponticum, Linne. 



From the Volga to Central Asia. This species, together with 

 R. Tataricuin (L. fil.), R. undulatum (L.), and a few others, 

 all Asiatic (one extending to Japan), provide their acidu- 

 lous leaf-stalks and unexpanded flower-mass for culinary 

 purposes. Rhubarb-leaves can also be used in the manner of 

 Spinage. 



Rhizopogon magnatum, Corda. 



Europe. One of the edible truffles sold in the markets of 

 Middle Europe, with E. rubescens, Tul. 



Rhododendron maximum, Linne. 



North-East America. Attains a height of 20 feet. Ir- 

 respective of its being a fine acquisition for any garden 

 copses, this bush seems of industrial importance, because Mr. 

 C. Forster asserts that the wood of this and the allied Kalmia 

 latifolia (L.) is equalled only by the best boxwood. This 

 may give a clue to other substitutes for that scarce commo- 

 dity, needed so extensively by the wood-engraver. 



Rhus caustica, Hooker and Arnott. 



Chili, where it is called the Litre. A small or middle-sized 

 tree, the very hard wood of which is used for wheel-teeth, 

 axletrees, and select furniture. The plant seems neither 

 caustic nor otherwise poisonous (Dr, Philippi) . 



