1518 



RHODODENDRON 



and if gentle bottom heat can be given after callusing 

 it will be of advantage. They root, however, but slowly, 

 except those of the Javanese kinds, which are mostly 

 propagated in this way, since they grow very readily 

 from cuttings. 



Layering is sometimes practiced, especially with the 

 dwarf and small-leaved species, but the layers usually 

 cannot be separated until the second year. 



For the propagation of the numerous varieties and 

 hybrids of hardv and half-hardy Rhododendrons graft- 



2105. Azalea Sinensis, to contrast with Rhododendron. 



ing is most extensively employed. Rhododendron 

 Catawbiense or seedlings of any of its hardy hybrids 

 may be used as stock; R. maximum is also probably 

 as good. In English and Belgian nurseries R. Ponti- 

 cum, which is inferior in hardiness, is mostly employed 

 as a stock, but this often proves fatal if the grafted 

 plants are transferred to colder climates. H. arboreum 

 may be used for strong-growing varieties intended for 

 cultivation in the greenhouse or south. Veneer- or 

 side-grafting is mostly practiced, and sometimes cleft - 

 and saddle-grafting (see G.C. 111.24:425). The leaves 

 should be removed only partly and the stock not headed 

 back until the following year. The grafting is usually 

 done late in summer or early in spring in the green- 

 house on potted stock without using grafting wax, and 

 the grafted plants kept close and shaded until the union 

 has been completed. If large quantities are to be han- 

 dled the plants are sometimes not potted, but taken 

 with a sufficient ball of earth, packed close together and 

 covered with moss. Covering with moss to keep the 

 atmosphere moist is also of much advantage if the 

 plants are potted. See Figs. 2107, 2108. 



Distribution of Species. About 200 species are 

 known, distributed through the colder and temperate 

 regions of the northern hemisphere; in tropical Asia 

 they occur in the mountains and extend as far south as 

 New Guinea and Australia, the greatest segregation 

 being in the Himalayas and E. Asia; several species 

 closely allied to those of the Malayan Archipelago are 

 found in the Philippine Islands, but are not yet intro- 

 duced ; 7 species occur in N. America. The species, with 

 few exceptions, are evergreen. 



Generic Description. Lvs. lepidote, sometimes lepi- 

 dote and pilose, or quite glabrous or tomentose beneath : 

 fls. pedicelled, in terminal umbel-like racemes, rarely 

 lateral in 1- to few-fld. clusters ; calyx 5-parted, often very 



RHODODENDRON 



small; corolla rotate-campanulate to funnel-shaped or 

 sometimes tubular, with 5-10-lobed limb; stamens 5-20, 

 usually 10: ovary glabrous, glandular, tomentose or lepi- 

 dote, 5-10-loculed : capsule separating into 5 valves con- 

 taining numerous minute seeds. The Rhododendrons 

 possess but few economic properties. The hardy close- 

 grained wood of the arborescent species is used for 

 fuel; also for construction and for turnery work; the 

 leaves of some species are sometimes used medicinally; 

 those of It. arboreum are believed to be poisonous to 

 cattle. The flowers of various species are sometimes 

 made into a subacid jelly. Some authors unite Azalea 

 with Rhododendron, but the two groups are very dis- 

 tinct horticulturally, however closely they may be allied 

 botanically. Azaleas are chiefly deciduous plants (A. 

 Indica mostly evergreen), usually with 5 exserted sta- 

 mens. Fig. 2105, Azalea Sinensis, also known as Rho- 

 dodendron Sinense, shows the difference in looks be- 

 tween the two groups. 



Hybrid Rhododendrons. Many hybrids have been 

 raised and they are now more extensively cultivated 

 than the original species. The first hybrid was prob- 

 ably the one raised from R. Ponticum, fertilized by a 

 hardy Azalea, probably A. nudiflora ; it originated 

 about 1800, in the nursery of Mr. Thompson, at Mile- 

 end, near London, and was first described and figured 

 as R. Ponticum, var. deciduum (Andrews, Bot. Rep. 

 6:379). Many hybrids of similar origin were afterwards 

 raised. The first hybrid between true Rhododendrons 

 was probably a cross between R. Catawbiense and R. 

 Ponticum, but it seems not to have attracted much at- 

 tention. It was by hybridizing the product of this cross 

 with the Himalayan R. arboreum introduced about 1820 

 that the first plant was raised which became the fore- 

 runner of a countless number of beautiful hybrids. 

 From the appearance of this cross obtained about 1826, 

 at Highclere, in England, and therefore called R. A Ita- 

 clarense, the era of Rhododendron hybrids is to be dated. 

 Figs. 2104 and 2106 are common hybrid forms. A sec- 

 ond era in the history of the Rhododendron may be dated 

 from the introduction of a large number of the beau- 

 tiful Sikkim Rhododendrons about 1850 and of the 

 Javanese species shortly afterwards. A third era will 

 perhaps be traced from the recent introduction of the 

 Yunnan Rhododendrons. ALFRED REHDER. 



HARDY RHODODENDRONS. Rhododendrons, in this ar- 

 ticle, mean the evergreen sorts, more particularly R. 

 maximum and the hybrid varieties of R. Catawbiense; 

 in the main, however, the directions for the various oper- 

 ations apply to the Azalea group and to many other 

 members of the heath family. 



Propagation. Rhododendrons are increased by seeds, 

 layers and grafts, and occasionally by cuttings. Seeds 

 should be sown under glass, between January 1 and 

 March 15, in soil one-half peat, one-half pure fine sand, 

 with good drainage. The seeds are small and require 

 no covering, the usual watering after sowing being quite 

 sufficient. A thin layer of sphagnum over the surface of 

 the seed-pan is good protection from the sun and keeps 

 the soil evenly moist; it should be removed when ger- 

 mination begins. Seeds may also be sown on growing 

 sphagnum, a thin layer being compactly spread above 

 the seed soil and drainage, and an even surface being 

 secured by clipping. Seed-pans or flats of convenient 

 size are used and they should be plunged in sphagnum 

 still further to insure even moisture; the temperature 

 of the house should be 45-50 F. Seedlings are prone 

 to damp-off and should be pricked-off into fresh soil as 

 soon as they are big enough to handle; wooden pincers, 

 made from a barrel hoop, are handy for this work. They 

 are slow growers and must be tended carefully. Keep 

 under glass, well shaded until the weather is settled. 

 Frames with lath screens make good summer quarters. 

 Winter in pits and plant out in frames in peaty soil when 

 large enough. Never let them suffer from dryness. It 

 has been suggested that the seed otR. maximum might 

 be planted on living moss under high -branched trees in 

 swamps where the water does not collect in winter. See 

 Jackson Dawson, on the "Propagation of Trees and 

 Shrubs from Seeds," Trans. Mass. Hort. Soc., 1885, part 

 1, p. 145. 



Layers probably make the best plants, and in the 

 best English nurseries layering is the common method 



