PRINCIPAL GROUPS OF PLANTS. 



39 



soap. It is also used to some extent in dermatology. In India it 

 has been used as a rubefacient. In Sweden, and among the 

 Chinese and Laplanders, Diatomaceous Earth has been used as an 



FIG. 20. The Algae are put to various uses by the people who collect them. The 

 illustration is taken from an ornament purchased at the Louisiana Purchase Exposition 

 and was made by the Filipinos from various kelps having large, bladder-like floats. 



edible earth under the name of " mountain meal " or " bread- 

 stone." Humboldt also calls attention to the fact (Aspects of 

 Nature) that the practice of eating earth is diffused throughout 

 the torrid zone, among indolent races inhabiting the finest and 



