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Stewartia pseudocamellia, A TREE FOR ALL SEASONS

Propagation
Fine plants may languish in a botanic garden, and not get out into the horticultural trade, because propagators haven't figured out how to grow them easily in quantity. Such was the case with the several species of Stewartia, a pity since S. pseudocamellia is one of the finest garden trees on earth.

This, the Japanese Stewartia, may reach 30 to 40 feet in cultivation, but slowly. Its flowers are creamy white with a boss of golden stamens and resemble a single camellia, which is not surprising since both genera are members of the tea family. Although each flower lasts only a day, there are many of them, as large as 3 1/2 inches in diameter, and they open from fat, silky buds over a period of weeks, beginning, in Boston, in late June or early July when the floral fireworks of spring are over and some fresh delight is wanted. The leaves are glossy dark green and turn yellow, red, or a dark reddish purple in the fall. One sees the handsome mottled bark to best advantage in winter, when one needs something good to look at in the garden.

IN AUTUMN DRESS

S. pseudocamellia grows wild in southern Korea as well as Japan. E.H. Wilson collected seeds of it there in 1917. The resulting trees were at first regarded as of a distinct species, S. koreana, and then as a variety of S. pseudocamellia. Arnold botanists now feel that the Korean tree is insufficiently different from S. pseudocamellia to deserve a different name. They acknowledge, however, that horticulturists, who may fibrillate over slight differences, prefer the Korean plant, finding it showier and hardier, and may persist in using some version of its name.

By any name, the tree grows well. It will take some shade in most climates and needs it in hot ones. It is, knock wood, not much visited by insects or disease. That may be because it has been little planted. When there gets to be a Stewartia in every yard, a plague of something will no doubt destroy them. Meantime, it is a leading citizen in the kingdom of plants.

But humblingly hard to propagate. Seeds are slow or unwilling to germinate. Cuttings root like weeds, but fail to grow out the following spring, then die. Once in the ground, Stewartia is finicky to transplant. Mortality increases as plants move through the several phases of production for nursery sales. No wonder nurserymen want little to do with Stewartia.

ITS SUMMER FLOWERS, LIKE SINGLE CAMELLIAS

Propagation research has been a strength of the arboretum since its beginning. Perforce. When Wilson came back from his explorations with pockets full of strange seed, the arboretum's propagators had to discover what to do with them.

Stewartia has a complex seed dormancy that the arboretum helped elucidate. The seeds require exposure to warmth for four months followed by cold for three. Then they may be sown. Cuttings are best taken when the tree begins flowering and should be treated with a certain rooting stimulant and fungicide. When the cuttings root, they ought not to be potted or they will go dormant, permanently. Leave them in flats, let them harden off, put them in cold storage until spring. Then pot them up.

Because the Arnold grows, at last count, 5,088 different kinds of plants, the staff has grown clever at propagation, and has kept meticulous records for decades. They have made a crucial contribution to horticulture by passing along their wisdom.

Ornamental Horticulture
Most of its visitors think of the Arnold Arboretum as a public park. They jog, walk the dog, cross-country ski, bird watch, picnic, smooch, and catch tadpoles in it. Indeed, it is part of the Boston park system. Harvard deeded the land to the city in 1882; in return, the city gave Harvard a 1,000-year lease on the property at $1 a year, with an option to renew for another 10 centuries. Harvard is responsible for the development, maintenance, and operation of the place; the city takes care of the walls and roads and provides policing. The arboretum is privately endowed as a department of the University, and its annual operating budget of $4.5 million comes largely from that endowment.

Charles Sargent collaborated with landscape architect Frederick Law Olmsted, LL.D. 1893,to design the road and pathway system and delineate the collection areas by genus and family. The living museum would be the brightest jewel in the Emerald Necklace, Olmsted's string of parkland from the Boston Common to Franklin Park. Recently augmented by 24 acres of wetland, the arboretum comprises 280 acres of varied typography, affording sweeping greensward, sylvan glades, and a view from Peters Hill of downtown Boston, surprisingly near, blessedly far.

Thousands of people come to the park on a special Sunday in May to revel in the arboretum's showiest set piece, the lilac collection, one of the largest in North America. Lilac Sunday presents the opulent bloom and delicious perfume of 600 specimens of 50 species and their botanical varieties and 250 cultivars of the genus Syringa. The oldest plant in attendance is S. reticulata, started in the Arboretum nurseries in 1876 from seed collected in Japan.

The genus is named after Syrinx, the Arcadian nymph. Pan pursued her and she fled into the River Ladon, where, at her own request, she was metamorphosed into a reed, of which Pan made his first flute. The late Father John Fiala, lilac guru, wrote that ancient Greek doctors used lilac stems to inject medications into patients or to bleed them. The first Europeans to settle America so loved the lilac that they brought bits of S. vulgaris with them and carried pieces cross country as they went. It is the state flower of New Hampshire and Idaho. So widely established is the lilac that people think it native although North America can claim not a single species. Lilacs are plants of eastern Asia, the Himalayas, and southeastern Europe.

While arboretum staff occasionally want to point out that there's more to the arboretum than lilacs, they are happy to indulge in pure ornamental horticulture on occasion. In 1978 propagator Jack Alexander ordered seeds of S. x chinensis from the Beijing Botanical Garden. One of the resulting seedlings is a substantial improvement over S. x chinensis hybrids generally available, and he has named it S. x chinensis 'Lilac Sunday'. Rooted cuttings will be on offer at the arboretum's annual plant sale in 1997 to help mark the Arnold's hundred-and-twenty-fifth birthday. If the public likes it, it will be available in garden centers sometime after the year 2000. "'Lilac Sunday' is an outstanding ornamental," says Peter Del Tredici. "The plant has smaller leaves and a more filmy overall effect than the common lilac. It is vigorous. It has long racemes of nice light purple flowers. It has no botanical significance. We didn't collect it from the wild. We have no idea where the parents came from. This is straight-up horticulture."

Hybridization
By nature botanic gardens are procurers and plants are promiscuous. Consider this case. In 1905 E.H. Wilson brought from China seeds of the Chinese witch hazel, Hamamelis mollis, and seedlings went into the arboretum's Hamamelis collection. There they kept company with other species, including H. virginiana, a native American, the plant from which early colonists made an astringent for treating aches and pains. H. mollis and H. virginiana merely nodded at each other because the former flowers in late winter and the latter in fall. But H. japonica, a winter flowerer, was also at the party. In nature the Chinese and Japanese witch hazels are separated by an ocean; in Jamaica Plain they were in bed together.

Hamamelis x intermedia,'ARNOLD PROMISE'

In 1928 the arboretum's propagator started seeds from one of their H. mollis plants. The resulting seedlings were not H. mollis. The pollen parent was eventually identified as a nearby H. japonica. Seven plants grew from these hybrid seeds. In 1944 they were christened H. x intermedia because their character was intermediate between their parents, as is often the case with hybrids. One of them was spectacularly different from its siblings and a far better plant than either of its parents. The arboretum gave it its own identity as the cultivar 'Arnold Promise'. It makes a vase-shaped shrub about 20 feet high. From mid-February well into March it is profusely covered with yellow, lightly fragrant flowers, each with four, ribbonlike, crinkled petals, seemingly fragile yet well able to withstand snow and ice. In extreme cold, the petals coil up like a spring, relaxing when the weather warms. The public didn't catch on to this splendid plant until the 1980s, but it is now ubiquitous.

"To maintain the collection, the arboretum goes back to the wild to collect new plants, or we clone our own plants asexually," says Del Tredici. "We are happy to distribute our seeds to other botanic gardens or nurseries. But if you collect seeds of one of our birches or oaks, for example, you never know what you'll get. You know the female parent, but the male could be anybody blowing in the wind."

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