NATIVE AMEKICAlSr SPECIES OF PRUNUS. 17 



their hybrids, more than 800 names, a development that has taken 

 place in less than 50 yeare. During the decade from 1890 to 1900 

 the increase in the number of varieties was exceptionally marked. 

 Many of these differ very little from each other and often are little or 

 no better, doubtless in some cases not so good, as those which may still 

 be found in a wild state. Dm'ing the last decade there has been perhaps 

 less interest, and probably only about 70 varieties of natives or their 

 hybrids were offered by the nursery trade in 1911. Too many 

 varieties have been produced without sufficient knowledge of the 

 distinguishing character of the species or of their relationships, and 

 a reaction has inevitably followed the feverish dissemination of new 

 varieties. In the beginning of horticultural development this is per- 

 haps unavoidable. Much pioneer work has to be done before a 

 basis for scientific development can be obtained, and now, after 50 

 years of work, the real substantial improvement remains to be 

 accomplished. 



SYSTEMATIC BOTANY. 



The botanical treatment given the species in the following pages 

 may perhaps be considered a broad one. There will always be 

 differences of opinion as to what constitutes a species, and the study of 

 a small amount of material which did not show the gradual varia- 

 tion from the aspect assumed by a species in one part of its range to 

 that assumed in another part might have led to different conclu- 

 sions. Fortunately, a large amount of material has been available. 

 Further study of the species in the field will contmue to afl^ord inter- 

 esting results concerning their variations and relationships, par- 

 ticularly in the Southern and Southwestern States. Many of the 

 species extend over a considerable range of territory. Most of them 

 are variable, but these variations have been very carefully considered, 

 and it is believed that to have established species on the slight differ- 

 ences that have sometimes served as the basis for proposed species 

 when a small amount of material was available would mean the 

 description of hundreds of forms — they can not be termed species — 

 and there would still remain hundreds of others intermediate in 

 character. 



The present treatment has been based on a study of nearly all the 

 species in the field, of more than 400 horticultural varieties, and of 

 the collections of the Bureau of Plant Industry, the United States 

 Xational 1 fcrljariuni, the Arnold Arboretum, tlie Gray Herbarium of 

 Harvard University, the New York Botanical Garden, the Missouri 

 Botanical Garden, the TTcrl^u-ium of the Geological and Natural 

 History Survey of Canada, the Xevv York Stale ((J(^neva) Agricultural 

 Experiment vStat ion , ( 'ornell University Agricultural Experiment Sta- 



74246'— Dull. 179—1.'; 2 



