(3) 



sand dried plants. Both may be freely consulted by anyone 

 interested. 



2. The names of plants in many eases have not become suffi- 

 ciently standardized to give any one name precedence over others. 

 All nomenclature and systems of classification are merely very 

 painstaking attempts on the part of botanists to systematize our 

 knowledge of over 160,000 different kinds of known plants. This 

 figure does not include possibly 150,000 different kinds of "flower- 

 less" plants, such as ferns, fungi, and algae. In the great major- 

 ity of cases the scientific name of a particular kind of plant is 

 sufficiently well established to carry no ambiguity as to what plant 

 it covers. Common names, on the other hand, are very frequently 

 misleading. It is a common thing for a tree to have a dozen differ- 

 ent popular names and for the same name to be applied to several 

 distinctly different trees. Scientific names have greater precision. 

 But even they, too, once in a while, are confusing. Standard books 

 on plants, however, usually list most of the scientific names by 

 which a plant has ever been known and this assists in applying 

 names correctly. 



The greatest confusion of names occurs, probably, in the many 

 horticultural varieties of Arbor-Vitae and "Retinospora." This 

 will be mentioned again in the descriptions of these plants. The 

 names given in this Guide have been selected more or less arbi- 

 trarily as best suited for the occasion. Ninety percent of them will 

 cause no confusion at all. 



A few definitions are in order here. The expression "species," 

 as generally understood and used in this Guide, means a particu- 

 lar kind of plant found wild somewhere on the earth. Since the 

 application of the term is purely man-made and since no two 

 plants, however similar, are exactly alike, there sometimes arise 

 questions as to whether or not two plants are sufficiently similar to 

 receive the same name. If, in the opinions of experts, and they 

 may differ, the differences are insignificant, then the two trees 

 are regarded as one. If the difference is somewhat greater, one 

 tree may be regarded as a variety of the other, and if their differ- 

 ences are great they are considered as two entirely different 

 species. 



