112 JOURNAL OF THE ARNOLD ARBORETUM [vol. ii 



bescence in C. panamensis is essentially lepidote, each tricliome having a 

 conspicuous, flat, brown centre. One of the panicles of the type specimen of 

 C. panamensis bears two bractlike leaves about 2 cm. long at the apex of 

 the peduncle. 



U.S. National Museum 

 Washington, D.C. 

 September 21, 1920 



NOTES ON NORTH AMERICAN TREES. VII ^ 



C. S. Sargent 



Pninus 



The last ten years have added little to our knowledge of the Plum-trees 

 of North America, where in the Arkansas, Oklahoma and Texas region they 

 are more numerous in species and probably in individuals than in any other 

 part of the world. It is diflBcuIt to obtain good material for a complete 

 study of these trees. They flower early when there is Httle else in bloom to 

 occupy the collector, who is obliged to make long and expensive journeys to 

 collect the flowers of one genus. In four years out of five the young fruit is 

 destroyed by the severe frosts which in that region usually come later than 

 the flowering of the Plum-trees, When the fruit escapes destruction by 

 frost it is difficult to obtain, for it ripens at the season when heat and in- 

 sects make plant collecting in the region where plums abound a difficult 

 and disagreeable undertaking. The diff'erent specimens are often widely 

 separated, and it is therefore impossible to make the comparative study of 

 the living plants which is necessary in order properly to understand their 

 similarities and differences. That there are natural hybrids between at 

 least some of the shrubby species is probable, but it has not yet been pos- 

 sible with available material to work these out; and there is little prospect 

 that American Plums can be properly understood until all or most of the 

 species can be grown together in one garden until they flower and produce 

 fruit. Such a collection will not be easy to establish and maintain, for some 

 of the most interesting species are not hardy in the north, and, except in the 



collect 



A good 



beginning of such a collection has been made by the Park Department of 

 the City of Rochester, New York, which has brought from Oklahoma and 

 Texas a large number of living plants of several species, varieties and prob- 

 able hybrids, and many seedlings have been raised from the fruit which has 

 ripened in Rochester on these plants. There are, too, a number of American 

 Plums in the Arnold Arboretum, although some of the Texas and Oklahoma 

 species which are doing well in Rochester have not proved entirely hardy 



here. 



Pnmus americana Marsh, is usually described as spreading by suckers 

 from the roots into large or small thickets. In the north this seems to be 



* For part vi, see Vol. i, p. 245, 



