THE AMERICAN BOTANIST 103 



Soap Plants. — Now that the war has caused an increase, 

 in even the price of soap grease, a lively interest is being mani- 

 fested in all sorts of saponaceous plants. One or two of these 

 soap-yielding- species have been articles of commerce for a long 

 time, notably the soap bark derived from the South American 

 trees, Pithecolobium bigcininum and Quillaia saponaria. A 

 stock of this bark is carried by most drug stores. The soap- 

 berry (Sapindns saponaria) is also used for washing clothes 

 in the tropics but a little soap goes a long way in such places. 

 The common bouncing Bet {Saponaria officinalis) gets its gen- 

 eric name from the soapy qualities of its juice, while its specific 

 name would indicate that at some time it, too, was sold in 

 shops. The substances in plants that give them their sapona- 

 ceous qualities are called saponins. They are really glucosides, 

 that is, substances which upon breaking up yield sugar and 

 some other substance. With water all saponins form a froth 

 or lather. Some are occasionally added to certain frothy 

 liquids to help out the froth, incidentally making" a barrel of 

 the liquid last longer. Saponins have been found in more than 

 a hundred species of plants. Among the plant families repre- 

 sented by saponaceous members are the Liliaceae, Dioscoreaceae. 

 Araceae, Chenopodiaceae, Phytolacaceae, Caryophyllaceae, 

 Berberidaceae, Magnoliaceae, Ranunculaceae, Bixaceae, 

 Theaceae, Rutaceae, Zygophyllaceae, Meliaceae, Polygolaceae, 

 Pittosporaceae, Rhamnaceae, Saxifragaceae, Passifloraceae, 

 Bignoniaceae, Leguminosae, Primulaceae, Sapotaceae, Ole- 

 aceae, Solanaceae, Schrophulariaceae, Rubiaceae, and Compo- 

 sitae. 



