172 A TEXT-BOOK OF BOTANY. 



On account of some of the saponin-containing plants being added 

 to beverages and used as emulsifying agents, the toxicity of a 

 number of the saponins has been studied, those which are highly 

 poisonous being known as sapotoxins. The following are some 

 of the plants which contain sapotoxin: Quillaja Saponaria (9 per 

 cent.), Agrostemma Githago (6.5 per cent.), Saponaria officinalis 

 (4 to 5 per cent.), and Polygala Senega (2.5 per cent.). 



Saponins have been found in more than a hundred different 

 plants, including one or more genera of the following families: 

 Liliaceae, Dioscoreaceae, Araceae, Chenopodiaceae, Phytolaccaceae, 

 Caryophyllaceae, Berberidaceae, Magnoliacese, Ranunculaceae, 

 Bixaceae, Theaceae, Rutaceae, Zygophyllaceae, Meliaceae, Simaru- 

 baceae, Sapindaceae, Hippocastanaceae, Melianthaceae, Polygalaceae, 

 Pittosporaceae, Rhamnaceae, Saxifragaceae, Passifloraceae, Big- 

 noniaceae, Myrtaceae, Rosaceae, Leguminosae, Primulaceae, Sapo- 

 taceae, Oleaceae, Solanaceae, Scrophulariaceae, Rubiaceae, and 

 Compositae. 



Gluco-alkaloids represent a class of compounds intermediate 

 between the alkaloids and glucosides, possessing characteristics 

 of each. To this class belong achilleine, found in various species 

 of Achillea, and also solanine, found in a number of species of 

 Solanum. 



FUNCTIONS OF ALKALOIDS AND GLUCOSIDES. In the growth 

 of the plant there must not only be an adaptation to the external 

 conditions and provision made to protect the plant against tem- 

 pests, drought, excessive light, extreme temperatures, etc., but 

 the plant must protect itself from diseases as well as from the 

 depredations of animals. As a rule, plants, particularly of the 

 tropics, depend on their own power to repair any injury to which 

 they may be subjected. Nevertheless, there are many plants 

 which produce poisonous substances, and these are usually sup- 

 posed to have the function of protecting them from various dis- 

 eases, as well as attack by herbivorous animals. Many of the 

 alkaloids and glucosides are apparently aplastic substances, i.e., 

 are formed either occasionally or continually as unavoidable by- 

 products of metabolism, or are produced for special purposes. 

 Some of these principles, as asparagine, an alkaloid, and hesperi- 



