84 PLANTS AND MAN 



all three have the leaves in the form of needles grouped in clusters; 

 a common bond of relationship which makes it possible to group 

 them all as pines. Such a group of related species is known as a 

 GENUS (plural, genera). Other common genera are the oaks, 

 maples and daisies; each a group of closely related kinds of plants. 

 In common terminology, when a double name — such as white 

 pine — is applied to a plant, the last name refers to the genus, the 

 qualifying adjective to the species. Common names, however, are 

 often indiscriminately applied to several different plants or may 

 be local appellations known only in a restricted area. Botanists 

 have found it necessary to give species and genera scientific 

 names which are always associated with a published and exact 

 description of the plant. A plant may have a dozen common 

 names, and in fact frequently does; but it has only one scientific 

 name, which is the same the world over. The scientific name is 

 also a double one, but in this case the genus name comes first, 

 instead of last. Thus the white pine is Pinus strobus, Pinus being the 

 name of the pine genus, and strobus referring to the species 

 known as white pine. The pitch pine, similarly, is Pinus rigida. 



A study of the characteristics of all plant genera shows that 

 some are quite like each other and are obviously closely related ; 

 the pines, spruces and firs have more traits in common than they 

 have with the maples. Such a group of related genera is known as 

 a FAMILY. And carrying the grouping further on the basis of 

 biologic kinship, an association of related families is known as an 

 order; related orders are grouped into a class; related classes 

 into a PHYLUM (plural, phyla). The phylum is the largest unit 

 used in classifying organisms, just as the species is the smallest. 



The larger the units of classification, the more obvious are the 

 characteristics by which they are differentiated from each other. 

 Differences among species, on the other hand, are often to be 

 detected only by professional botanists. It is easier, for example, to 

 tell two different genera — such as oaks and maples — ^from each 

 other, than to tell a red oak from a black oak (two different 

 species) . Likewise it is easier to recognize the differences between 

 the pine family, which includes the firs and spruces, and the 

 cypress family, which includes the cedars and junipers; than to 

 differentiate between a spruce and a fir, each of which is a genus. 



