for July, 1920 



257 



Notes from the Arnold Arboretum Bulletin 



Japanese Azaleas. 



THE flora of Japan contains many species of Azaleas, and in 

 early Spring their brilliant flowers enliven innumerable hill- 

 sides. Many species and varieties are favorite garden 

 plants in Japan, and Japanese gardens owe much to these plants. 

 In distribution the Azaleas of Japan are generally southern, 

 and only a few species are found in the northern part of the em- 

 pire. All of the species will probably flourish in the southern 

 United States ; and many of them will succeed as far north as 

 Long Island and possibly in Newport, Rhode Island. Of the 

 si.xteen Japanese species three are well established and hardy in 

 the /\rboretum ; a northern species, Rhododendron (all Azaleas 

 are now called Rhododendrons by botanists) Albrcchtii related 

 to our Rhodora but with red flowers, judging by the climate of 

 the region in which it grows, should also be hardy here. This 

 handsome plant, however, which was first raised at the Arboretum 

 twenty-five years ago, has not been a success here. Another 

 northern species. Rhododendron Tschoiioskii. with the smallest 

 flowers of any Azalea, is an old inhabitant of the Arboretum but 

 is still without value as an ornament of gardens. Two beauti- 

 ful Azaleas from the mountain forests of central Hondo, Rliodo- 

 di-ndron Rrhdcrianuni and R. pcntapliyllunt, have not yet been 

 sufficiently tested in the gardens of this country ; they may be 

 expected to be able to bear the cold of Massachusetts Winters, 

 but appear diflicult to establish. Another Japanese Azalea, R. 

 mucroiiatum, generally known as Acalca Icdijolia or as A::(.ilea 

 indica alba, has been seen in American gardens for the last eighty 

 years. It is very often found in the old gardens of the southern 

 states; it is hardy and often cultivated on Long Island, and oc- 

 casionally lives for many years in sheltered positions in eastern 

 Massachusetts. The three Japanese species, which have proved 

 themselves, after a trial of twenty-five years, to be perfectly 

 hardy and first-class garden plants in eastern Massachusetts are 

 R. K(cnipfcr't, now considered a variety of R. obtusuni. R. 

 japonicum and R. rrticuUttuin. better known as R. rlionibiciiin. 

 The first of these plants is the only red flowered Azalea which 

 is hardy in this climate. Thousands of seedlings have been raised 

 in this country in recent years and it will soon become common 

 in eastern gardens. It has been largely used in the Arboretum, 

 and late in May and in the early days of June its flowers fur- 

 nish the most surprising and spectacular display of the year. 

 The flowers are delicate, however, and when fully exposed to 

 the sun lose their color ; and this Azalea gives most satisfaction 

 when it is planted in the shade of trees or on the northern border 

 of a wood of conifers. In the Arboretum the most successful 

 group of thi.s Azalea is behind the Laurels (Kalniia) and in front 

 of the Hemlocks at the northern base of Hemlock Hill. The 

 plants bloom a week later than those in more exposed situations 

 and their flowers last much longer in good condition. The 

 tallest plants in the Arboretum are now eight or nine feet high 

 and although growing in complete shade never fail to flower. 



Rhododendron japonicum has been growing in the .\rboretum 

 as long as Krempfer's Azalea, and by many persons it is con- 

 sidered a handsomer plant. It is a round-topped rather coni- 

 pact shrub usually not more than three or four feet tall, with 

 flame-colored flowers three inches across. It is only in recent 

 years that the value of this plant in American gardens has been 

 recognized, for it was long supposed, in the Arboretum at least, 

 to be one of the numerous forms of the short-lived and usually 

 unsatisfactory hybrids sent to this coimtry chiefly from Holland 

 and known commercially as Acalca mollis. A beautiful yellow- 

 flowered variety of /\. japonicum (var. atirciim) has been found 

 in Japan, and a few plants have reached the United States, where 

 two years ago it flowered for the first time in a Massachusetts 

 garden. Tins plant promises to be an important addition to the 

 number of hardy .\zaleas which can be grown in this climate. A 

 handsome race of hybrid Azaleas was obtained several years ago 

 in Europe probably by crossing Rhododendron japonicum with 

 the yellow-flowered .\zalea of eastern China, usually known as 

 R. sincnsc. To this race of hybrids the general name of A'. 

 Kostcrianum has been given. The best known plant of this hybrid 

 origin is probably the one called "Antony Koster." It is a hand- 

 some plant, but not always entirely hardy in this clim.-ile where 

 it is usually short-lived. About eight years ago T. D. Hatfield, 

 gardener of the Hunnewell Estate at Wellesley, Massachusetts, 

 crossed A', japonicum raised from seeds collected by Professor 

 Sargent in Japan with R. sincnsc raised from seeds collected by 

 Mr. Wilson in eastern China. There can be no doubt about the 

 parentage of this plant. This new Azalea, which has been named 



R. Kosterianum, "Miss Louisa Hunnewell" bears large clusters of 



orange-colored flowers which open as the leaves unfold ; the plant 

 is perfectly hardy, and the flower-buds were not injured by the 

 exceptionally severe Winters of 1917-18 and 1919-20. If anyone 

 in the United States has raised a handsomer shrub it is unknown 

 '.o the Arboretum. During the last seventy-five years several 

 hundred different hybrid Azaleas have been made in Europe and 

 the LTnited States ; accurate and reliable records of the parentage 

 of these hybrids, however, have not been kept, and published 

 statements of their parentage are often mere guesswork. Cer- 

 tainly many of these hybrids have been obtained by crossing not 

 only species but hybrids. This mingling of plants, themselves 

 often of unknown or uncertain origin, has produced difficulties 

 of determination which no amount of study w-ill probably ever 

 overcome ; and of all hybrid Azaleas the parentage only of this 

 Wellesley plant is really known, a fact which certainly adds to 

 its value and interest. 



Early-Uoztxrcd American Azaleas. Before the flowers of 

 Rhododendron I'ascyi have entirely faded those of the two most 

 widely distributed species of eastern North America, R. nudi- 

 ilorum and R. canesccns, begin to open. These plants are com- 

 mon from New England to Texas : they have pink, very fragrant 

 flowers which open before and as the leaves emerge from the 

 bud, and very similar in general character, will perhaps some- 

 time be considered varieties of one species. They have been 

 planted in considerable numbers in the Arboretum and grow 

 equally well in open borders or in the partial shade of woods. 

 Before their flowers fade those of the flame or yellow-flowered 

 .\zalea (R. calendulaccum) of the Appalachian Mountains, the 

 most splendid of American Azaleas, will begin to open. 



LatE-FI.O WEEING ViBURXUlIS 



The Aboretum late in June owes much of its beauty 

 to the late-flowering Viburnums of the northeastern states 

 which have been planted here in considerable num- 

 liers. The first of these plants to bloom and the handsomest of 

 them. Viburnum cassinoides. although it grows naturally in cold 

 northern swamps, takes kindly to cultivation, and in ordinary 

 garden soil is a handsomer and more shapely plant than it is in 

 its natural home where it often makes slender straggling stems 

 fifteen or twenty feet tall. The beauty of this Viburnum is in its 

 ample, thick and lustrous leaves which vary in shape and size 

 on different plants, in its broad convex clusters of pale cream- 

 colored flowers and in its large showy fruit w-hich when fully 

 grown is yellow, then pink, and finally blue-black, the three colors 

 often appearing at the same lime in the same cluster. The fruit 

 of Viburnum cassinoides is larger than the bright blue fruit of the 

 other Summer-flowering species, V. dentatuni, V. venosum and V. 

 Canbyi which bloom in the order in which they are mentioned 

 here. They are large round-topped bushes with coarsely toothed 

 leaves and lar.ge clusters of white flowers ; they are all good 

 garden plants and respond to generous treatment with more 

 vigorous growth, a better habit and handsomer foliage. There 

 is a large collection of deciduous-leaved V'iburnums in the 

 Arboretum and there is now a good opportunity here to judge 

 the comparative values of the plants from different countries, 

 and this comparison shows that the flora of eastern North 

 -America contains more handsome garden plants in this genus 

 than all the rest of the world. In Japan there are species like 

 Vibrunum tomeitlosum, V. Sieboldii and ]'. dilatatum which are 

 beautiful garden plants, and the Eurojiean Traveler's Tree. V. 

 lanlana. is one of the handsomest and most distinct of the early- 

 flowering Viburnums which can be successfully grown here. In 

 claiming the superiority of the American species for American 

 gardens it must be remembered that none of these species have 

 red fruit, which is produced by several of the eastern Asiatic 

 species. The most successful of the red-fruited species in the 

 .•\rI)orclum have been V. dilatatum and F. Jl'ri.shtii. These 

 should find a place in .American collections, especially the former 

 winch is here a hardy, free-flowering plant of compact habit, 

 which has few rivals in the beauty of its brilliant and abundant 

 bright red fruit. 



The Horse-Chestxuts 

 .lesoilus :.;eorgiana is covered again with its compact clusters 

 Tf large red and vellow flowers. The southern Buckeye has not 

 been injured by the severe Winters of 1917-18 and 1919-20. and 

 is certainly one of the best new plants which have been brought 

 into our gardens in recent vears. When first discovered it was 



