NATIVE AMERICAN SPECIES OF PRUNUS. 17 
their hybrids, more than 800 names, a development that has taken 
place in less than 50 years. 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 inawild state. During 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 characters 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 botanicat 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 continue to afford. 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 
~hen a small amount of material was available would mean the 
“escription 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 
National Herbarium, the Arnold Arboretum, the Gray Herbarium of 
Harvard University, the New York Botanical Garden, the Missouri 
_ Botanical Garden, the Herbarium of the Geological and Natural 
History Survey of Canada, the New York State (Geneva) Agricultural 
Experiment Station, Cornell University Agricultural Experiment Sta- 
74246°—Bull, 179—15——2 
