POLYGOtfUM. 199 



The Asclepiads number 146 genera and 1300 species, most abun- 

 dant in S. India, S. Africa, and Australia. There are comparatively few 

 species in the United States. 



Butterfly-weed, or Pleurisy Root (Asdepias tulerosd), a handsome 

 plant with orange-colored flowers, native in our pastures and meadows, 

 is employed medicinally as a laxative and diaphoretic. 



DiscMdia, of E. India, is a famous Pitcher Plant. 



The Cow Tree of Ceylon (Gymnema lactiferum) yields a bland, whole- 

 some milk which the natives use for food. 



The Wax Plant (Hoya), from the W. Indies, with wax-like leaves 

 and umbels, is a favorite house plant. 



Stapelia, with flowers so foetid as to deserve the name "Carrion 

 Flower," is a large S. African genus.* 



The Record of A. incarnata, another species quite com- 

 mon, is here annexed as a model for the order. 



Scientific Terms. Coma. Corona. Gamopetalous. Hoods. 

 Horns. Pollinia. 



LIV. SPOTTED KNOTWEED. 



Description. In June, and after, the Spotted Knotweed 

 displays its flesh-colored spikes. Like the other foreigners, 

 it seeks cultured fields and the waste corners about our 

 dwellings ; and the garden which is free from its encroach- 

 ment is well kept. None favors the intruder, yet the bot- 

 anist may profit by the study of its wonderful organization. 



Analysis. The 3toot. We first note that the root is 

 axial in its kind, and a cross-section shows but one woody 

 layer ; hence it is annual. The stem is remarkable for the 

 distinctness of the internodes, the nodes being excessively 

 swelled, and looted with the stipules. 



* This plant is sometimes cultivated in the green-house for the pake of its gro- 

 tesque branches and pretty flowers. So carrion-like is its odor that the common 

 blue-bottle fly is said often to make the mistake of "blowing " it, i. e., of depositing 

 its eggs upon the petals, where they occasionally hatch, but only to starve, 



