CLII. DICHONDEE^E. 



567 



Convolvulacea are chiefly tropical; they decrease northwards, and are very rare in our climate, and 

 absolutely wanting in the arctic regions and on mountains. Many species possess a milky juice contain- 

 ing a highly purgative resin ; this resin, which especially abounds in the rhizome, owes its properties 

 solely to the presence of an aromatic principle ; for rhizomes which have been pulverized and long ex- 

 posed to the air lose it, although preserving the purely resinous principle. The species most in use are 

 Jalap {Convolvulus Jalapa and C. Schiedeanus), from Mexico [the best is from Exogonium Purga]; the 

 Turbith (C. Turpethuni), a native of the East Indies; Scammony (C. Scammonia and C. sayittcefolius'), 

 from the Asiatic Mediterranean region [and the Ipnmoca pandurata of the United States]. The 

 rhizomes of our indigenous Bindweeds are also purgative, but the exotic species are much more active. 

 The American genus Batatas comprises several species in the rhizomes of which (called Sweet Potato) 

 the resinous principle is replaced by an abundant quantity of starch, and they are thus sought for as a 

 food similar to potatos. [Convolvulus disseotus is said to abound in prussic acid, and to be used in the 

 preparation of Noyau. Oil of Rhodium is the produce of the rootstock of Rhodorhiza. ED.] 



CLII. DICffONDRE^E* 



(CoNVOLVULACEAKTJM genera, Endlicher.) 



This little family may be considered as a tribe of Convolvtilacece, with which they agree in the insei 4 - 

 tion, regularity, and isostemony of the corolla, the number of carpels and of the erect anatropous ovules, 

 the mucilaginous albumen, and the contortuplicate cotyledons ; it has been separated on account of its 



Dichondra. 

 Flower cut vertically (mag.). 



Dichondra repens. 



Dichondra. 

 Corolla and andi-ceciiim laid open (mag.). 



Dichondra. 

 Single oarpel (mag.). 



Dichondra. 

 Carpel cut vertically (mag.). 



