PRINCIPAL GROUPS OF PLANTS. 



119 



fir; Pseiidotsuga mucronafa or Douglass Spruce (Red fir) is prob- 

 ably the source of a balsam resembling Canada turpentine and 

 which is known commercially as Oregon balsam. Picea mariana 

 or black spruce yields spruce gum, largely used in the manufacture 

 of chewing gum, and is also the source of spruce beer. Picea 

 excelsa or Norway spruce yields Burgundy pitch. Abies alba, 

 white fir or silver fir yields the Strasburg turpentine. Canada 

 pitch is the resinous exudation from the common hemlock 

 (Tsuga canadensis). Sandarac is yielded by Callitris quadrivalvis 

 found growing in Northwestern Africa. Volatile oils are yielded 

 by a number of the Coniferae, of which the following may be 

 mentioned: Jiiniperiis Sahina yielding oil of savin; Juniperus 

 communis yielding oil of juniper, both of which are used in medi- 



FiG. 77. Microscopical view of fragments of wood found in the coal deposits of upper 

 Silesia, Prussia. — After Link, from article by Potonie on the origin of coal and petroleum 

 in Ber. d. d. pharm. Ges., 1907, p. 181. 



cine. The remains of Coniferae {Picea, etc.) are often found as 

 fossils, as the fossil resin amber, wdiich is used in the arts, and 

 on distillation yields a volatile oil having medicinal properties. 



Angiosperms, General Characters. — They constitute the most 

 conspicuous portion of the flora, embrace the greatest variety of 

 forms, and are the most highly organized members of the plant 

 kingdom. They vary in size from diminutive plants like the 

 windflower to the giant oak which shelters it. They may accom- 

 plish their life work in a few months, as the common stramonium, 

 or they may persist for several hundred years, as the trees of our 

 primitive forests. They may inhabit dry desert regions, as the 

 Cacti and Chenopodiaceae, or they may live wholly in water, as 

 the water lilies. In short, they show the greatest adaptability 



