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~GAZ.NE JOURNAL OF THE AMERICAN HORTICULTURAL SOCIETY, INC. * April 1960 AMERICAN HORTICULTURAL SOCIETY A union of the American Horticultural Society and the American H orticultural Council 1600 BLADENSBURG ROAD) NORTHEAST. WASHINGTON 2, D. C. For United Horticulture *** to accumulate) increase) and disseminate hm"ticultural information B. Y. MORRISON) Editor Directors T erms Expiring 1960 JAMES R. HARLOW) Managing Editor DONOVAN S. CORRELL T exas Editorial Committee CARL W. FENNINGER Pennsylvania W. H. HODGE, Chairman W. H . HODGE Pennsylvania JOH N L. CREECH A. J . IRVING FREDERIC P . L EE New York WILLIAM C. STEERE CONRAD B. LINK New Yo rk CURTIS MAY Tenns Expi1'ing 1961 FREDERICK G . MEYER STUART M. ARMSTRONG WILBUR H. YOUNGMAN Maryland JOH N L. CREECH Maryland WILLIAM H. FREDERICK, JR. Officers Delawa1'e FRANCIS PATTESON-KNIGHT PRESIDENT Virginia RICHARD P. WHITE Washington, D. C. DONA LD WYMAN Massachusetts F IRST VICE· PRESIDENT T enns Expi'ring 1962 DONALD W YMAN Jamaica Plain, Massachusetts FREDERIC P. L EE Maryland H ENRY T. SKINNER SECOND VICE-PRESIDENT District ot Columbia STUART M. ARMSTRONG GEORGE H . SPALDING Silver Spring, Maryland California RICHARD P. WHITE SECRETARY-TREASURER District ot Columbia OLIVE E. WEATHER ELL ANNE WERTSNER WOOD Washington, D. C. Pennsylvania The American Horticultural Magazine is the official publication of the American Horticultural Society and is issued four times a year during the quarters commencing with January, AprIl, July and October. It is devoted to the dissemina tion of knowledge in the science and art of growing ornamental plants, fruits, vegetables, and related subjects. Original papers increasing the historical, varietal, and cultural knowledges of plant materials of economic and aesthetic importance are welcomed and will be published as early as possible. The Chairman of the Editorial Committee should be consulted for manuscript specifications. Reprints, saddle-stapled, will be furnished in accordance with the following schedule of prices, plus postage, and should be ordered at the time the galley proof is returned by the author: One hundred copies-2 pp $6.60; 4 pp $12.10; 8 pp $25.30; 12 pp $36.30; Covers $12.10. Entered as second class matter in the post office at Baltimore. Maryland. in accordance with the Act of August 24. 19 12. Additional entry for Washington, D.C., was authorized July 15, 1955. in accordance with the pro­ visions of Section 132 .122, Postal Manual. A subscription to The American Horticultural Magazine is included as a benefit of membership in the American Horticultural Society. Individ ual Membership dues being 16.00 a year. APRIL. 1960 FORI'vIERLY THE NATIONAL HORTICULTURAL MAGAZINE VOLUME 39 • NUMBER 2 Contents Rhododendron Species for the Sma ll Home Garden H. H. DAVIDIAN _____ _________________________________________________________________________________________ 61 Echeveria ERIC "\,tv AL THER 73 Daphnes CLARENCE VAN HOUTEN __________________________ .. ___________________________________________________ 92 Culitvated Philippine Mussaendas MONA LISA STEINER _________________ .. ____________________ ___ ___________________ _________________________ _ 98 Blackspot and Powdery Mildew of Roses JOHN G. PALMER and T. J. HENNEBERRY _____ .____________________________________________ 108 A Book or Two _________ .__ .._____________ ....________________________________________________________________________ III T he Gardeners' Pocketbook Magnolia wilsoni. J OHN L. CREECH _____________ ____________________________________________ 116 Pumice Rocks. FREDERICK W. COE __ _________ _____________ _______________________ ____________ 117 Rutherford Hybrid Azaleas. NIRs. R. G. STAPLETON __________________________ __ 117 Two Uncommon African Members of the Mint Family D. G. H UTTLESTON ________________________________________________________________________________ 120 Magnolia coco. FREDERICK W. COE ____ __________________________________ . ____________________ 122 APRIL COVER ILLUSTRATION (ERIC WALTHER) A close-up view of the foliage of Echeve'ria lalani . one of the hundreds of photographs Eric Walther made of the Echeveria he grew and found in their native h omes . See details on Page 73 Cot)yright 1960 by The A merican H orticult.ural Society, I nc. C L.AUDE H OPE Rhododendron impeditum rNAT URA L SIZE) Rhododendron Species For the Small Home or Rock Garden H. H. DAVIDIAN the history of plant introduction, George Forrest explored Yunnan and Szechuan, and in the course of seven expeditions to western China, he enriched our rock gardens with a large number of rhodo­ dendrons. Several other species and new Rhododendrons, which grow from a forms were sent by various other collec­ few inches up to about three feet and tors, including Farrer, Rock, Kingdon­ which are particularly well suited for the Ward, and Ludlow and Sherriff. small home or rock garden, are amongst The vast majority of these plants are the important and popular plants in natives of western China and the Hima­ present day horticulture. laya, where they grow at elevations of It may be of interest to give a brief eight to about seventeen thousand feet, note on the history of introduction of and are found in varied habitats. Some these low-growing species. The first spe­ of the species of the Lapponicum Series cies introduced into cultivation in 1656 are said to cover the moorlands iust as was RhododendTOn hiTSutum, from the heather does in the British moorlands. European mountains. The next was R. In cultivation these low-growing spe­ ferTugineum, which is said to have ar­ cies provide color from January or Feb­ rived about a hundred years later. A ruary until July or August. but most of few more were added towards the end of them are in flower from the middle of the eighteenth and in the nineteenth April to the middle of June. cen turies. Between the years 1848-1851 Although a great number of species Toseph Hooker was responsible for the present themselves for consideration, ref­ introduction of several species from the erence will be made in this account to Himalaya, and during the latter half of a large selection which are ideally suit­ the ninetenth century the F!ench Mis­ able for the small home or rock garden. sionaries made some funher contribu­ tions from southeast Tibet, southwest Anthopogon Series Szechuan, and northwest Yunnan. A few One of the most remarkable in this others were received from Ernest H. Wil­ Series is Rhododendron sarRentianum, a son during his exploration of western native of western Szechuan, from whence China early in the present century. In it was introduced by Wilson in 1903. It the year 1904, which is a landmark in is a compact shrub up to two feet high with aromatic foliage, and makes a won­ derful show with its yellow or white flowers produced freely, in clusters of six to twelve. The plant is hardy, a robust grower, and is easy to cultivate. Familiar to many gardeners IS R. · !\'[r. H. H. Davidian is a taxonomist on the staff of the Royal Botanic Garden, Edinburgh, cephalanthum, discovered in 1884 by Scotland. He is the leading taxonomist on true Delavay in Yunnan near Lankong and rhododendron species and a contributor of Hokin. It is fairly widespread in west­ numerous articles on rhododpndrons in British ern China and Upper Burma at eleva­ horticultural publications. The Royal Botanic tions of nine to fifteen thousand feet. Garden of Edinburgh grows, under rock ~arden cnn(l;tion~. the world's finest collection of dwarf This wide distribution and altitudinal rhododendrons. rang·e explains the great variability of [61] 62 THE AMERICAN HORTICULTURAL MAGAZINE the species in habit and height, in leaf Boothi Series shape and size, and in flower color. One of the earliest of all rhododen­ Amongst the several forms in cultiva­ drons to burst into bloom is R. leucaspis, tion, one which is compact and wide an outstanding plant, discovered by spreading bearing a profusion of pink Kingdon-Ward in 1924 at lVlusi La, in flowers in clusters of eight toO twelve, is the Tsangpo Gorge, Tibet, at ten thou­ of great beauty and generally considered sand feet. It is compact in growth, up to be the best. The variety crebrefiorum to two feet high or more, with large is a compact shrub up to eight inches rounded or obovate leaves up toO two high, and is greatly admired when cov­ inches long, and is extremely charming ered with rose-pink flowers in April or when adorned with large, pure white, May. A close ally is R. primulaefiorum, single or paired flowers. The plant is uncommon in cultivation. This plant is easy of cultivation, but as it flowers in upright in growth up to three oOr four February or March, disappointment is to feet in height with rigid branchlets, and be expected, for the flowers and flower­ attracts attention with its white, pink or buds are sometimes completely destroyed by early spring frosts. Otherwise it is rose flowers. It is perfectly hardy, is easy hardy, and well deserves the Royal Hor­ of cultivation, and is worthy of being ticultural Society's Award of Merit widely grown. which it received in 1924 and the First Another member of this Series is R. Class Certificate in 1944. A near ally is anthopogon, introduced into cultivation R . megeratum, "lovely in the highest de­ in 1820 from the Himalaya where it is gree," with openly bell-shaped or saucer­ widely distributed at elevations of nine shaped yellow flowers, usually in single to sixteen thousand feet. It is an inter­ or paired clusters. It is a compact shrub esting plant with large aromatic leaves or sometimes straggly and spreading, which are said to be used as incense in with rounded leaves, very glaucous be­ --r:ibetan monasteries. The plant is a neath. Although hardy, it is particular VIgorous grower up to eighteen inches as to position in the small home or rock high, with pink flowers produced in garden. To obtain the best results, some April or early in May. The closely related shade and protection from wind are es­ R. hyp.enan.th.um,.

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