METHODS OF CLASSIFICATION 99 



ficially and arbitrarily created to aid in classifying, are species. 

 As the usual unit in botanical classification, this group must have 

 more particular consideration. 



141. Species. — A species is a continuing succession of like in- 

 dividuals. This definition seems to give species a permanency 

 which they do not possess, and must be qualified by the state- 

 ment that all species are derived from other species and from all 

 may develop still other species. A species may not be a natural 

 but a man-made group delimited from series of plants in the 

 attempt to classify in accordance with the best light at the 

 moment, but with the expectation that when more is known 

 about the plants the groups called species may be reformed. 

 The only object in making species is to group the plants on the 

 earth so that those who work with them, whether agriculturist, 

 forester or botanist, may do so more conveniently. The word 

 species is either singular or plural. 



142. Varieties. — Individuals in a species are assumed to show 

 close similarity in all essential characters. No two of them, 

 however, as has been said, are exactly alike. Variation is found 

 in all species. When there are groups of variant forms in a 

 species growing in the wild, such an assemblage is a botanical 

 variety; or, and more particularly when the variation is well 

 marked and certainly known to be hereditary, a sub-species. 

 Thus, in Prunus americana, the American plum, a group is 

 readily distinguished by the amount and character of pubescence 

 on the leaves and is, therefore, set off as a botanical variety, 

 P. americana mollis, the w^oolly-leaved plum. Classifiers often 

 differ as to whether a certain group should be called a species 

 or a variety. There is no way of settling the disputes. Usually 

 the opinion is accepted of the man who is considered the best 

 authority on the plants classified. 



Those who cultivate plants use the name variety to distinguish 

 seed and vegetative variations from botanical varieties, often to 

 the confusion of those employing the terms. Strongly marked 

 variations of farm and garden crops coming true to seed are 

 seed varieties. Sorts of onions, peas, beans, wheat, corn, or 

 clover are listed in seedsmen's catalogues as varieties. These 

 seed varieties are commonly annuals or sometimes biennials. 



The sorts of tree, bush, vine, and small-fruits, as well as many 



