jtay Heroarmm arvard UnWetsity ARNOLD ARBORETUM HARVARD UNIVERSITY ARNOLDIA A continuation of the Bulletin of Popular Information VOLUME XI •951 PUBLISHED BY THE ARNOLD ARBORETUM JAMAICA PLAIN, MASSACHUSETTS Digitized by the Internet Archive in 2017 with funding from BHL-SIL-FEDLINK https://archive.org/details/arnoldiaarno_8 A ARNOLDIA A continuation of the Bulletin of Popular Information of the Arnold Arboretum, Harvard University Volume 11 MARCH 9, 1951 Number 1 FORTY-FIVE OF THE BEST SHRUBS FOR MASSACHUSETTS GARDENS* There are actually thousands of different kinds of shrubs growing in Massa- chusetts gardens today, but many of these are decidedly inferior to others from an ornamental vieM’point. Just which ones are best will always be a debat- able question. Some are meritorious for autumn coloration ; some make far better hedges than others ; still others are superior for spring bloom. No two people will ever agree on a small list of the best shrubs (the smaller the list the more the disagreement!) Even with these points clearly in mind, the plants discussed on the following pages are offered as among the best shrubs for Massachusetts gardens. First, however, before scrutinizing the list, it should be understood that there are several ‘‘old stand-bys” that will always be most serviceable. New shrubs may be glowingly discussed in the catalogues, but these old-fashioned favorites have served reliably for many years and probably will continue to do so for many more. These are among the plants which every gardener should know and use, for one reason or another. Nothing is meant to be implied in the discussions of the forty-five “selected” types, that would cast a shadow of doubt on the service- abiliCv of these. A few are listed on page 20. With the above-mentioned “common” shrubs clearly in mind, let us consider some that are more unusual, either not used as frequently in gardens as they might be or are more difficult to find in nurseries. It should be emphasized that some Massachusetts nurseryman has indicated in 1951 that he has plants of each * This list was prepared at the request of the Horticultural Committee of the Garden Club Federation of Massachusetts, five of the plants to be discussed at each of the nine meetings of horticultural chairmen throughout the year. Because of wide-spread interest in this list, it is here reproduced for the benefit of ARNOLDIA subscribers. It is not perfect and many will take exception to it. However, it does include 45 top-notch shrubs that can be used more in our gardens today. Most important, all are available in 1951 from local nurseries! [ 1 ] ) one of tlie varieties listed (two exceptions only), available for sale in 1951, and those sources are ‘jiven. It is useless to become enthusiastic about a plant that is unobtainable. Not so this list of forty-five. Every one is grown and offered for sale in 1951 by some easily available nurseryman (and there are other nursery sources on the record, outside the state, where these plants can be obtained like- wise). Consequently, the gardeners of the state are urged to become acquainted with some of the shrubs in the following list in 1951, to purchase and use a few that they do not know already, and in this wa,v increase their knowledge of good plants as well as improve the beauty of the plantings about their homes. Forty-five of the Best Shrubs Recommended for Massachusetts Gardens Berberis julianae 2, 5, 7, 10, 11 ‘ ‘ koreana 1 , 3, 4, 5,6 Buxus microphylla koreana 2, 4, 5, 6, 8, 11 Chionanthus virginicus 1, 2, 3, 4, 5, 6, 7, 9, 10, 11 Clethra alnifolia rosea 4, 5, 10, 11 Cornus alba sibirica 1, 2, 3, 4, 6, 7, 9, 10 Cotoneaster dammeri 5, 6, 11 “ divaricata 2, 4, 6, 8 Cytisus praecox 2, 4, 5, 7, 8 Enkianthus campanulatus 1, 2, 4, 5, 7, 8, 9, 10, 11 Euonymus alata compacta 1, 2, 4, 5, 6, 7, 8, 9, 11 Fothergilla sp. 2, 4, 5, 6, 7, 8, 11 Hamamelis mollis 5, 6, 7, 8, 11 vernalis 1, 2, 4, 5, 6, 7, 8, 9 Hypericum sp. 1, 2, 5, 6, 8 Ilex crenata convexa 1, 2, 5, 6, 7, 8, 9, 10, 11 Juniperus chinensis sargenti 2, 4, 5, 6, 7, 8, 9, 10 Leucothoe catesbaei 1, 2, 3, 4, 5, 6, 7, 8, 9, 11 Lonicera amoena arnoldiana 5, 6 bella 1,6 korolkowi floribunda 1, 4, 5, 6, 7 Magnolia stellata 2, 3, 5, 6, 7, 8, 9, 11 Mahonia aquifolium 2, 5, 6, 7, 8, 11 Malus sargenti 1, 2, 3, 5, 6, 7, 8, 9, 10, 11 Philadelphus lemoinei “Avalanche” 6, 7, 9, 10 “ splendens 6 Pieris floribunda 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 japonica 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 Potentilla fruticosa 6, 7, 8 Rhododendron arborescens 1, 2, 4, 5, 7, 8, 9, 10 calendulaceum 1, 3, 4, 5, 6, 7, 8, 9, 10, 11 [2] Rhododendron gandavense 9 “ mucronulatum 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 “ schlippenbachi 1, 2, 4, 5, 7, 8, 9, 11 “ smirnowi 4, 9 [ “ vaseyi 1, 2, 4, 5, 7, 8, 9, 10, 11 I Rosa multiflora 1, 4, 6, 7, 10, 11 J Syringa persica 1, 2, o, 6, 7, 8, 9, 10 “ prestoniae 5, 6 I Taxus cuspidata nana 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 Tsuga canadensis pendula 5, 7, 8 diversifolia 5, 7, 9 Viburnum dilatatum 2, 3, 4, 5, 6, 7, 8, 10, 11 I “ sieboldi 1, 3, 4, 5, 6, 7, 8, 10, 11 i “ tomentosum 2, 5, 6, 7, 8 Sources for Shrubs Listed 1. Adams Nursery, Inc., Westfield, Mass. ( 2. Bay State Nurseries, North Abington, Mass. 3. Cherry Hill Nurseries, West Newbur.v, Mass. 4. Harlan P. Kelsey, Inc., East Boxford, Mass, i 5. Kingsville Nurseries, Kingsville, Maryland 6. Henry Kohankie & Son, Painesville, Ohio 7. Littlefield-Wyman Nurseries, 227 Centre Avenue, Abington, Mass. 8. Weston Nurseries, Inc., Weston, Mass. - 9. Wyman’s Framingham Nurseries, Framingham, Mass. 10. Lexington Nurseries, Inc., 1266 Massachusetts Ave., Lexington 73, Mass. 11. Tingle Nurseries, Pittsville, Maryland Forty-five of the best shrubs for Massachusetts gardens Berberis julianae 6' Zone 5 Wintergreen Barberry A very dense growing, hardy, evergreen barberry. This is one of the few bar- berries not susceptible to the black stem rust of wheat and hence it is allowed to be grown and sold freel.v. It should have some winter protection in the coldest parts of the state, and might well be used in evergreen foundation plantings where some protection is usually available. There are other evergreen barberries I that are as good or possibly even better, but this one is available. Its spiny ever- green leaves, delicate yellow bell-like flowers and blue fruits combine to make it an interesting plant. Berberis koreana 6' Zone 5 Korean Barberry This deciduous Korean Berberry is rapidly proving itself in gardens and nurse- ries throughout the eastern United States as a perfect substitute for the some- [3] what taller and certainly more common barberry {B. vulgaris). This latter is one of the many species which is an alternate host for the devastating wheat rust, and it is these that the U.S. Department of Agriculture is passing legislation against so that it is becoming increasingly difficult for commercial men to grow them. In this case, the Korean Barberry is a perfect substitute, with its small, pendulous fruit clusters of bright red berries in the fall and its fiery red autumn foliage coloration. It makes an excellent barrier plant as well as a fine specimen. Buxus microphylla koreana 3-4' Zone 5 Korean Box This is the hardiest of all the boxwoods. Because of the gardener’s inherent desire for boxwood in plantings, even in New England, this variety may have merit. Admittedly there are several cions of the true English Box {Buxus semper- Virens) that have shown indications of hardiness in New England under varied climatic conditions, but until these are propagated on a wide scale and thoroughly tested under all of New England’s tough growing conditions, one might do well, if box must be grown, to confine one’s efforts to this species. As time goes on, it may well be that some of the many cions above-mentioned will replace this variety in popularity. Chionanthus virginicus 30' Zone 4 Fringe-tree This native Fringe-tree makes a fine ornamental, either as a large shrub or as a small tree. Its fleecy white flowers are produced in the utmost profusion. Usu- ally the sexes are separate with the staminate flowers the larger. One word of caution should be given, for since this plant is closely related to the lilacs, it is also susceptible to the same scale infestations. These should be rigidly controlled. Especially does this make a well-rounded specimen plant in the full sun where it seems to grow best. Some Europeans consider this one of the most striking of the American shrubs introduced into Europe. The fruits are large and grapelike, and the brilliant yellow autumn color is outstanding. Its leaves appear late in the spring, one of the last plants in the xA.rboretum to produce leaves. Even with this drawback, it makes a splendid specimen where it can be given plenty of room. Clethra alnifolia rosea 9' Zone 3 Pink Summersweet Either this variety or the species makes an excellent addition to the garden for summer bloom and fragrance. Not many shrubs bring forth deliciously fragrant flowers in the summer and the narrow spikes of the Summersweet are most beauti- ful. The flowers of the species are white, and this variety has flowers that are tinged a light pink. Sometimes they gradually fade white. If the pink-flowered form is not essential, don’t overlook the species, a native along the New England coast. It tends to grow in clumps and it increases by underground stems. If the PLATE I Ct/fisH.s praero.r, the Warminster Broom. An excellent shrub for dry sandy soils, with pale, lemon yellow floweis in mid-May and ^reen stems all winter. soil is too dry, there may be some dantyer from an infestation of red spider, which - can be controlled, but in moist soils it is at its best. Native American plants J should be exploited in our gardens to the utmost, and this is one that apparently . has not been used as much as it should. Cornus alba sibirica 9' Zone 2 Siberian Dogwood 'I'liis variety does not spread as rapidly as does our native C. stolonifera, and this fact should be kept in mind so that it is not planted in borders and expected to r “take over,” as is C. stolonifera. However, the Siberian Dogwood has stems the J winter color of which is the brightest red of any shrub available. Unfortunately it has become mixed in American nurseries, with some of the lesser brilliant red- stemmed forms, but the real plant is excellent for winter color. It is best to prune > it heavily every third year or so, even cutting the planting to the ground in the early spring, so that the young shoots will grow vigorously. It is these that are the brightest colored. Its numerous white flowers in late May, and white to bluish i berries in the early fall, are additional reasons why it should be grown. Cotoneaster dammeri \' Zone 5 Bearberry Cotoneaster f Lower in habit than C. horizon! alis^ this makes an excellent ground cover or rock . garden plant. It is not recommended in place of C. horizontalis but only in situ- • ations where a lower plant of this type is desired. Its bright red berries are most i conspicuous in the fall. Cotoneaster divaricata 6' Zone 5 Spreading Cotoneaster i The arching, spreading habit of this 6' Cotoneaster is outstanding. The branches are covered with small bright red berries each fall. The leaves are only f" long i and in the experience of several Massachusetts commercial growers, this species is easily among the most reliable for the state. Cytisus praecox 6' Zone 5 Warminster Broom i If dry soil or very poor soil is present in the garden, where few other things will grow, the chances are the Brooms will thrive. This one in particular is rec- ommended because of its hardiness (more hardy than the Scotch Broom which! has been naturalized on the Cape) and because of its green twigs, that actually give the plant an evergreen appearance in the winter. It grows in a very dense manner, with minute leaves, but its pale yellow pea-like flowers appear in mid- May in the greatest profusion. It should be noted that large plants are hard to move. To avoid disappointments, buy small plants, preferably in pots, and set them out in spring in their permanent situation. [6] Enkianthus campanulatus Zone 4- Redvein Enkianthus 30' An ericaceous shrub requirinor the same type of cultural conditions as azaleas and rhododendrons, but differing in having small bell-shaped flowers in mid-May and brilliant scarlet autumn color. The flowers appear just before the leaves and so are easily seen. A good acid soil plant, not used nearly enough in our gardens. Euonymus alata compacta 1' Zone 3 Dwarf Burning Bush Everyone knows the Cork Bush, but this compact, dwarf form is one that should prove just as well known. It originated in the Adams Nursery in West Spring- field in 1926, and only now is becoming widely available. It makes a splendid dense, rounded specimen and has been used in hedges requiring no clipping if sufficient room is available. When space is limited, it can be easily restrained with clipping every other or even every third year. One of the specimens grow- ing in the Arnold Arboretum colors so vividly every autumn that it is easily among the best of all the plants there for fall color. ' Fothergilla species 3-9' Zone 5 Fothergilla There are several species available from different nurserymen, varying chiefly in height at maturity. All have interesting, white, thimble-like flowers in mid- spring, and all have an excellent yellow and red autumn foliage coloration in the fall, especially when grown in the full sun. If in the shade, neither flowers nor autumn coloration are quite so marked. However, in a foundation planting, es- pecially with an evergreen background, these American natives can be kept re- , strained and still be among the most ornamental plants during the two seasons when they are at their best. They are rather difficult to propagate except by seed, one of the reasons why the nurserymen fail to grow them in large quanti- ties, but from the standpoint of the home gardener, they are certainly worth ' seeking out ! Hamamelis mollis 30' Zone 5 Chinese Witch-hazel This Witch-hazel has the largest flowers of the group, and they are fragrant i as well — hence it niakes a desired garden specimen. Its flowers with unique ribbon-like petals, and its brilliant yellow autumn color, are its chief reasons for two-season interest. It can easily be kept controlled with judicious pruning. Hamamelis vernalis 10' Zone 5 Vernal Witch-hazel There are several Witch-hazel species available, but this one should be better known. It is an American native, with deliciously fragrant small flowers in late winter — actually it is the first woody plant to bloom. It is vigorous in growth, : needs almost no attention, and like others in this group has bright j ellow fall [7] color. Altlioujrh tlie Chinese Witch-hazel has larger flowers, this Vernal Witch- hazel makes a fine bush and is hardier, being amenable to all sorts of pruning and restraint, especially by the over-anxious gardener who likes to force things indoors. Hypericum sj)ecies Ground Cover to 6' Zone 4-7 St. Johnsworts 'riie St. Johnsworts are low woody shrubs, sometimes ground covers, valued for their bright yellow flowers. Some of them, as they grow tall, will have a very interesting shiny brown exfoliating bark of considerable ornamental value in the winter. The ground covers, especially, are frequently avid growers and can ciuickly crowd out other low plants in the rockery if not restrained. Their fruits are dry capsules and have little autumn coloring. However, a splendid feature of this group, especially the ground covers, is the fact that they grow well in dry, sandy soil. Some of them, like Hypericum prolificum, continue to produce flowers over many weeks in the summer and, of course, summer-flowering shrubs, especially those with bright yellow flowers, are none too numerous. These plants should not be overlooked for the small garden especially since several species are available commercially to fit several types of situations. If summer bloom amongst the shrubs is not particularly needed, the shrubby types might be passed over, but the ground covers have merit regardless. Ilex crenata convexa 15' Zone 5 Convex Leaved Japanese Holly The best New England substitute for Box. As stated previously, some garden- ers may want to try the true Box or one of its many so-called hardy” cions. For those who do not want to take this chance, this small leaved evergreen is the perfect substitute. One plant in the Arnold Arboretum now is easily 7' tall and at least twice as broad without a dead branch in it. Like other varieties of this species, it is easily pruned and can be used in hedges, but as a specimen plant, untouched by the pruning shears, it makes an excellent well-shaped specimen. Juniperus chinensis sargenti Ground Cover Zone 4 Sargent Juniper Certainly not a new plant to American gardens, but one that could well stand more general use. It is a low, prostrate ground cover, found in seashore areas in its native habitat in mats 8-10' in diameter. Its steel blue color difl^ers from that of most junipers used for ground covers. Leucothoe catesbaei 6' Zone 4 Drooping Leucothoe An American native, it is black-listed in New England sometimes merely be- cause people do not know how to care for it properly. It may grow as high as 6' in its native habitat, but in New England it should be kept much lower — mostly under three feet. Whenever it is severely injured by a hard winter it might well [8] i j be cut to the ground and started all over again. The lustrous dark green leaves ! in summer are reason enough why it should always be kept growing vigorously, and the bronze autumn color of the foliage lends value to any evergreen founda- tion planting in tlie winter. In si)ots where some winter protection is available, especially some shade during late February and March, the foliage will not be burned as much as wiien the plant is grown with full exposure to sun and winds, d'lie small racemes of waxy white Howers borne on the under side of arching stems repay anyone for taking a few pains in providing the right growing conditions and winter protection. Lonicera amoena arnoldiana 9' Zone 5 Arnold Honeysuckle A very graceful floriferous shrub, it is meritorious for the arching habit of its branches as well as its delicate foliage. Since honeysuckles are not susceptible to serious disease pests, it is well to know a few others than the one or two com- mon species that are planted so much. Lonicera bella 6' Zone 4- Belle Honeysuckle Several cions occur in this hybrid species that cause this group to be one of the most floriferous and most fruitful of all. Either for massing or for specimen use these plants have merit. The early summer fruits are, like other Loniceras, very bright and attractive to birds. Lonicera korolkowi floribunda 12' Zone 5 Blue-leaf Honeysuckle Either the species or the variety (they are very likely mixed in many nurseries) are outstanding for their bluish to grey-green foliage color, adding considerable color variation in the shrub border throughout the entire growing season. It must be noted here that this is one species, as opposed to all the other honeysuckles, that is apparently difficult to establish, but once growing well, it is a worthy addition to the plant population of any garden. Magnolia stellata 20' Zone 5 Star Magnolia Actually a tree, but easily grown as a shrub even on the small property. The white, fragrant, star-like flowers appear in late April as first among the Magno- lias. It also is the hardiest and the only one with a good bronze autumn color when grown in the full sun. Its dense habit of growth, splendid green foliage and autumn color make it a valued addition to the larger shrubs available for Massachusetts planting. Mahonia aquifolium 3' rarely 6' Zone 5 Oregon Holly-grape This is perhaps the most popular of the Pacific Northwest plants now grown in the East, yet it could be used more. Its lustrous dark green, leathery leaves. pyramidal spikes of bright yellow flowers and light-blue grape-like fruits in early summer, make it effective for use in many situations, especially in evergreen foundation plantings and in shaded spots It does well in poor soil and can be kept low by proper pruning Its spiny, holly-like evergreen leaves are interest- ing and its method of increasing by underground stolons insure its use as a ground cover of fair height. Malus sargenti 6' Zone 5 Sargent Crab apple The lowest of all the crab apples, included here for it seldom grows over 8' in height, this is a crab apple that can be used on the small grounds. It usually grows twice as broad as high, and, of course, has two seasons of colorful interest, because of profuse white flowers in May and dark red fruits in the fall. Philadelphus lemoinei “Avalanche” 4' Zone 5 This excellent little variety is only about 4' tall, with single white flowers 1" in diameter and a fine arching habit from which the plant takes its name. Philadelphus splendens 8' Zone 5 Of excellent habit, this is another mock-orange that can be used as a specimen if desired for it is well clothed with branches to the ground. The flowers are borne in groups of five with conspicuous yellow stamens, but they have only mediocre fragrance. In some situations sacrifices can be made in the fragrance of the flowers in order to have a plant that is symmetrical and well branched. Pieris floribunda 6' Zone 4 Mountain Andromeda One of the most serviceable of all broad-leaved evergreens in the North be- cause it seems to do well in any normal soil and has no serious pests or diseases. The erect to nodding clusters of white flowers are composed of numerous small waxy flowers similar in size and shape to those of the blueberry. The flower buds are prominently evident all winter long — somewhat of a conspicuous promise that spring-blossoming time is just around the corner. Pieris japonica 9' Zone 5 Japanese Andromeda An excellent broad-leaved evergreen for the same reasons P. floribunda is pop- ular. In addition, the Japanese Andromeda has a lustrous dark green foliage and flower clusters that are pendulous. A well-grown specimen of the Japanese An- dromeda, covered with lustrous leaves and pendulous flower clusters, is about as beautiful an evergreen as it is possible to grow. In New England it should be grown in protected places, but farther South this is unnecesary. Young foliage is usually a rich bronze in spring, later turning a normal green. This species can [ 11 ] be jrrown in a sliacled situation, but like many other plants, will not produce as many flowers there as in situations with more sun. Potentilla fruticosa Zone '■Z Bush Cinquefoil Many varieties of this species have been found over a wide area of the north- ern hemispheres. 'I’he sturdy, very hardy plants, bloom in mid-May and continue throujrhout summer, sometimes even into September. Because of its compara- tively low height, its lack of interestin ARNOLDIA i A continuation of the Bulletin of Popular Information of the Arnold Arboretum, Harvard University V^oLUME 11 APRIL 27, 1951 Number 3 MFTASRQUOIA BROUGHT UP-TO-DATE The history of the discovery of Metasequoia glyptostrohoides has been retold several times. In short, it is this. In 1941 the genus Metasequoia was de- scribed by Miki, a Japanese botanist, on the basis of fossil material found in Korea and Japan. Mr. Tsang Wang of the Central Bureau of Forest Research in China, first collected specimens in 1944, not knowing what they were. In 1945, Mr. C. L. Wu, another Chinese botanist, in examining these collected specimens, realized that they represented a genus that was very unusual and probably new. These specimens eventual!}’ came into the hands of Dr. W. C. Cheng of the National Central University, Nanking, and Dr. H. H. Hu of Fan Memorial In- stitute of Biology, Peiping. They were recognized as belonging to the previously described fossil genus Metasequoia. To make certain, an expedition was organized in 1946 to collect fresh material which Cheng and Hu later described in 1948 as Metasequoia glyptostrohoides. To all these Chinese botanists goes the full credit for the discovery of this heretofore ‘^extinct” species. When botanical specimens were examined by Dr. P7 D. Merrill, former Director of the Arnold Arboretum, in the latter part of 1946, he became interested in attempting to obtain seeds. Accordingly, a modest grant was sent to Dr. H. H. Hu, who sent out an expe- dition for this purpose on September 3, 1947. This expedition returned with seeds, the first ones of which arrived at the Arnold Arboretum on January 5, 1947. T>r. Merrill ami the Arnold Arboretum should he given credit for the introduction of this species into modern gardens., for this first lot of seeds was distributed far and wide throughout the world. Later, additional seed lots were also sent to the Arbore- tum, as well as to institutions on the Pacific Coast. Because of great popular interest in the story surrounding the discovery of this species, many articles have appeared concerning it. The best bibliography of these to date appears in An Ecological Reconnaisance in the Native Home of Metasequoia glyto.stroboides’’’* by Kwei-ling Chu and William S. Cooper in Ecology, Vol. 31, No. 2, April 1950, pp. 260-278. [ ] Metasequoia has exhibited very fast growth. The photograph on page 27 shows how a 28-month-old specimen has grown eight feet from seed in England. Speci- mens in this country may not have grown quite so fast, although one plant in the Santa Barbara Botanic Garden grew five feet in one year. As mentioned above, considerable has already been written about this tree and its origin, but requests keep coming in continually for more information concern- ing it. For detailed facts, the above-mentioned bibliography, and especially the article to which it is attached, will give the complete story. A few points of practical interest here, may help to bring many up-to-date.” At first it was thought that this species might not be hardy north of Georgia. The climate of the coastal plain in Georgia is very similar to that of the native habitat of this tree. Recent investigations have shown that it is growing in a small section of Szechuan and Hupeh Provinces in China (near Chungking) where the annual rainfall amounts to about 48'', rather evenly distributed throughout : the year. Here also very little snow falls, and though there may be some, native 1 reports are to the effect that it does not amount to much. Temperatures on the ■ average apparently do not go much below freezing. Just why this species should : be confined to this small area of not over 300 square miles will make a most in- teresting story when all the facts are known. Suffice it to say that the atmosphere in this area is reasonably moist and that 1 several soil tests show the soils to be about neutral to only slightly acid. Appar- : ently no accurate records are available on the lower temperatures in the winter, and summer temperatures are not supposed to average over 100^° F. The tree has ; been found to be reseeding itself in moist ravines, in what might be considered ; the same kind of places where we would expect hemlocks to reseed themselves in this country. Since its introduction, it has been living out-of-doors unprotected in several f places on the Pacific Coast. Here in the East it has survived in Washington, |; D.C., Philadelphia, New York and Boston, living out-of-doors uninjured the last i three winters without protection. All reports are not yet available and many i seeds and plants have been distributed, so that some may have been injured within this area. It should be pointed out that these three winters have been i' comparatively mild ones, and no prolonged sub-zero weather has occurred. It ! would be advisable not to become too enthusiastic concerning the hardiness of i this species, certainly not until we see what happens to older trees when unusu- i ally cold winters occur. Practical plantsmen can have a field day in discussing the possibilities of hardi- I ness. Many variable factors like soil, rainfall, high temperatures, low tempera- ' tures, exposure and length of growing season affect the hardiness of a plant. In i the case of a new plant, where climatic records of its habitat are meagre (as in this case), one should proceed slowly in drawing conclusions concerning its hardi- : ness on the basis of three mild winters only. However, for those practical plants- I men willing to do some guessing, it will be of much interest to know that Chu , and Cooper found the following plants native to the same location as the Metase- quoia. Incidentally, all of these are hardy in the Arnold Arboretum. [ ] PLATE VIII Metasequoia glyptostrohokies. A 28-month-old specimen grown in a coldhouse at Bramley, Surrey, England, and now 8' 3" high. Kalopanax pictus Lonicera japonica M orus alba Parthenocissus tricuspidata Quercus acutissima variabilis Uhamnus utilis Spiraea japonica Styrax japonica Viburnum setigerum Akebia trifoliata Cercidipliylluin japonicum sinense Corn us controversa Corylopsis sinensis Cotoneaster liori/ontalis Decaisnea farjjesi Kuonyinus alata Helwingia japonica Hibiscus syriacus Idesia polycarpa However, before said practical plantsmen wax overly enthusiastic concerning hardiness of this new species, the following plants are also growing in the same location. These are not hardy in the Arnold Arboretum. Actinidia chinensis Liquidambar formosana Camellia oleifera Lonicera pileata Cunninghamia lanceolata Nothopanax davidi Ficus heteromorpha Nyssa sinensis The tallest specimens of this tree in China are about 100 feet high. Estimates have been made from borings in the trunk that some of these trees may be 300 years old. It is obviously a rapid-growing tree, certainly while young, but it should also be emphasized that apparently everyone growing it in America has given it optimum growing conditions. The wood is rather brittle, and is not ap- parently used for any special purpose except for fuel, by the natives in the vicinity of the native stands in China. It apparently grows best in a moist atmosphere, with soils that contain a good deal of moisture. It is obviously loose and open in habit, and may be best suited for growing in groves rather than as individual specimens, although many in this country, at least, will grow it for a long time as single specimens merely because of its interesting history. It should be remembered that this species is not an evergreen and in this re- spect certainly not like the giant redwoods of our Pacific Coast. It is deciduous, and in its native habitat does not grow to the great size and age of our native redwoods. The name “Dawn Redwood” is most misleading, intimating a close association (at least to the general public) with the giant redwoods of the Pacific Coast that actually does not exist. It is easily propagated by cuttings. There are a sufficient number of plants growing in America now, so that even though the seed source may be cut off, commercial propagation of this plant can easily be worked up to supply the de- mand in a short time. Either soft wood or hard wood cuttings root readily. Al- though many nurserymen have it in America, there are three, at least, who already list it as availabe in their catalogues. These are : Rare plant Club, 208 McAllister Avenue, Kentfield, California Tingle Nursery, Pittsville, Maryland Verhalen Nursery Company, Scottsville, Texas These notes should be of value to all those amateurs interested in the latest information concerning this tree. Donald Wyman Tn.^ 1, — 4 — y ARNOLDIA A continuation of the Buli.etin of Popular Information of the Arnold Arboretum, Harvard University Volume 1 1 MAY 11, 1951 Number 4 THE LARZ ANDERSON COLLECTION OF JAPANESE DWARF TREES i 4 fT^HE Larz Anderson collection of Japanese dwarf trees presented to the A Arnold Arboretum as a memorial to his friend, Charles Sprague Sargent,” is an explanatory statement quoted from the carved inscription displayed with these intriguing plants. This group of dwarf trees is unique in this country and was received at the Arboretum in the fall of 1937. The plants have been on public display in a specially erected shade house ever since. Brought to this country at a time when strict plant quarantines were not in force, these plants were imported with soil around the roots in their original Japanese containers. The Arboretum welcomes the opportunity of being able to display these striking examples of Japanese horticulture to its visitors. The honorable Larz Anderson became interested in Japanese horticulture as early as 190? and built a particularly attractive Japanese garden on his estate in Brookline, Massachusetts. Somewhat later he became interested in dwarf trees and in 1913 he brought back from Japan a splendid collection of them, which he acquired while serving as Ambassador Extraordinary from the U nited States to Japan (1912-1913). These he placed on dis])lay in his own garden where they were carefully tended for twenty-five years by different Japanese gardeners. The collection has been displayed at several exhibitions in Boston where it invariably ; won high honors. I This unique collection is displayed in its lath house between the old Bussey ; Institution building and the greenhouses, fairly close to the hedge collection. Around the shade house have been planted a few shrubs and trees native to Japan, and during the next few years it is planned to augment this planting. The collection now installed in the shade house consists of 29 specimens all im- I ported in 1913. They are well labelled, but for those unable to visit the collection (the house is open from 9:00 a.m. until 5:00 p.m. each day except Saturday, Sunday and liolidays) the names of the individual plants and their respective ages are given below. Name of plant Age Chamaecyparis obtusa 213 years < ( < « 163 148 44 ( < < < 118 44 ii 88 4 4 i ( 63 4 4 Acer Buergerianum 98 4 4 “ palmatum 63 4 4 63 44 < < < i 58 4 4 <4 4 4 58 4 4 4 4 4 4 53 4 4 4 4 4 4 53 4 4 44 4 4 53 4 4 4 4 4 4 48 4 4 “ “ multifidum 53 44 Cryptomeria japonica 48 4 4 Larix leptolepis 138 44 Photinia villosa laevis 68 44 Prunus mume 98 4 4 4 4 4 4 88 4 4 “ subhirtella 98 44 4 4 4 4 88 4 4 4 4 4 4 78 44 Thujopsis dolobrata variegata 43 4 4 << << << 43 44 Zelkova serrata 88 4 4 44 4 4 Chamaecyparis pisifera squarrosa\ 63 4 4 Cryptomeria japonica > Euonymus fortunei radicans / 43 “Bon-sai,” the art of training dwarf trees Century old customs have been handed down by the Japanese regarding the j training of the interesting dwarf trees so characteristic of the gardens and homes [ of that country. There are several reasons for their existence. In the first place, | Japanese and Chinese gardens are usually small, for space is at a premium. This : is particularly true in the urban areas where the art of making gardens on a very small scale is centuries old. Then, too, the oriental’s well known appreciation ; of the aesthetic value of living plants has been a prime factor in their cultivation. It often takes fifty to one hundred years to grow a worthy specimen dwarf tree, yet it is possible by twisting the trunk and restraining the growth of tops and roots to give a comparatively young plant the appearance of great age. This [30] PLATE IX Chamaecyparis ohtusa. 163 years old. (Larz Anderson Collection.) treatment re(|uires a tliorouj^h knowledjje of hortieulture as well as painstakinjr patienee, but many Japanese are faseinated with “Bon-sai“ and praetiee it as a pastime. Training Most woody plants can be dwarfed if given the proper training. If the branches and roots of growing plants are vigorously restrained from developing rapidly, the individuals soon become dwarfed and this is the principle underlying all training. 'I'hen, too, great care is given to the training of the trunk, the spread of the branches and their shape, and the spread of the roots, since each can be so trained as to give the impression of great age. Many methods have been de- vised through the centuries for attaining these ends. Maples, bamboos, cherries, pines, hollies, oaks, azaleas, junipers, and many other plants have been used. They are grown in comparative!}' small containers, kept pot bound throughout their existence, and carefully and judiciously pruned to maintain the desired type of growth. Whenever possible, the Japanese start with plants that have already been dwarfed by nature. These are searched for in the high mountains, in regions often unfamiliar to the ordinary traveller. Such plants are frequently found grow- ing in high rocky crevices, just barely existing for lack of sufficient nourishment. If these are dug immediately and removed, they might succumb at once for the delicate balance between the amount of root system and bare existence is easily upset. The plant hunter may locate such plants several years before he will ven- ture to remove them from their rocky dwelling. At first he will prune a small portion of the plant and leave it in place for a year; then he will return and root prune another small portion, repeating this process until it is safe to move the plant. In this way splendid specimens are obtained that have already been trained with the assistance of mother nature herself. If dwarf plants are to be trained from the seedling stage, the smallest and weakest seedlings are selected. Conifers are considerably easier to train, for they do not form adventitious buds as readily as do the broad leaved plants. The seed- ling is placed in a very small pot. If there is a tap root, it is pruned considerably, and if a central leader is present, it too is cut back. In order to obtain the de- sired effect, only certain branches are allowed to develop. As an example, Cham- (lecyparis ohtusa is ordinarily a very bushy plant, yet the illustration shows only a few picturesque branches. These few branches have been carefully selected and trained, while the others have been entirely removed. If one of these branches should die, eventually a new bud would be allowed to develop a branch to suffi- cient size to take the place of the deceased one. To give the correct appearance of wind-contorted shape, the main stem is often twisted around an upright, and after a formative period the upright is removed, 'fhis twisting in itself is a dwarfing process, since frequently it breaks a large number of the conducting vessels in the stem. Branches are twisted in like man- [32] 1 I I I i I 1 i 1 i 1 i i ( I i PLATE X Finns Jeffrey i in Yosemite National Park has been continually dwarfed by nature for an estimated (>()() years. ner. I'liey may all be trained on one side of the plant, or arranged to droop on one side of the pot, or trained in any one of a dozen different ways. The Japanese gardener usually has a model in mind when he trains his plant, some wind- twisted tree which he is trying to reproduce in miniature form, and it is surpris- ing to the uninitiated to observe how accurate these reproductions can be. Often in nature one observes old gnarled trees the larger roots of which are exposed, especially when growing in rocky places where there is still soil. This effect is reproduced by the “Bon-sai*’ artist by growing his seedling in charcoal and moss for a period sufficiently long to induce long roots. When the plant is removed to its permanent container, a part of these roots are left to develop ; above the soil level, eventually aiding materially in giving the plant the appear- ance of great age. Pruning, Repotting and Watering Not all branches are entirely removed. Some of these century old plants have numerous picturesque stubs, certain gardeners believing that these add to the beauty of the plant. Any diseased tissue on such stubs is carefully scraped, dis- j infected, and painted. Sometimes in order to gain the appearance of stubby old age rapidly, taller plants that have been growing normally are used. The basal branches are cut back to give the stubby appearance. The top is entirely cut off. The plant is dug and after many of the roots have been removed it is placed in ; a small pot. Then certain of the adventitious buds are allowed to develop, or else scions are grafted at the desired places. Grafting is also resorted to when certain shoots die. If a very important branch has died, it may take many years for a new one to grow to a sufficient size from | an adventitious bud, so that grafting is often resorted to. The Japanese are par- I ticularly adept at this and take great pains in training an individual branch ‘by pinching the buds back here, or twisting the branch there, and so forcing the latter to grow in the desired fashion. The pruning and pinching operations are tl done during the active growing period, since the development of branches from adventitious buds is then more frequent. Dwarf trees are repotted every four or five years for two reasons. In the first ; place it is necessary to remove some of the newly developed fibrous roots so that | the tree will remain dwarfed. Secondly, it is necessary to mix a small amount ' of fertilizer with the soil, since as these trees are forced to grow in very small I containers, there is not sufficient room for enough soil to allow new root develop- ment unless the plant be artificially stimulated with nutrients. It is also advisable to keep a fresh layer of green moss on the surface of the soil. This not only adds the impression of age, but keeps the soil from drying out. The containers are usually provided with a hole in the base for proper drain- age. In the hot summer days there is some danger of the soil becoming too dry, and at such times the plants need special attention. Spraying the foliage with [ ] water once or twice a day during the hottest spells of summer is advisable in order to keep the plant in good condition. Dwarf trees cannot be considered primarily as indoor plants. They may be used indoors for short periods, but must be grown in the open a greater part of the time. Because of their very small root system, and the small containers in which they are grown, these dwarf trees cannot lose much water through tran- , spiration and still survive. Consequently they must be grown in a shaded loca- tion. The shade house in which this location is being maintained at the Arbore- tum was designed and erected especially for this purpose. Constructed of cypress wood, the top and sides of the house are covered with strips inches wide with similar spaces left between each strip. This supplies plenty of shade and at the same time keeps the atmosphere considerably cooler and reasonably moist. Winter Protection Although many of these trees are hardy, they cannot survive our northern winters because of their shallow root system, unless given some winter protec- tion. A Japanese maple, for instance, growing normally in the ground may sur- vive a winter during which the temperature goes to 20° below zero although the i top of the plant may be killed to the ground. However, in these small pots the • roots of dwarf trees would be subjected to temperatures almost as low as those of the surrounding atmosphere, and consequently the whole plant would be killed. During the winter in the north, they are best put in cold frames or pits which are well protected with glass and even with boards and mats during the most severe weather. In our pit where these plants were stored last winter the temperature did not go below freezing, although the temperature outside the pit dropped to zero on several occasions. Another danger from freezing temperatures is that with the expansion of freezing soil the containers may break. Although these are seldom ornate, since the Japanese believe that the plant itself should ' be the point of interest, nevertheless their simplicity alone is beautiful and makes them important adjuncts to any such collection and thus worthy of full protection. Thus with an exacting knowledge of the numerous rigid requirements of the art of ‘‘ Bon -sai” the painstaking Japanese gardener is able to reproduce dwarf trees that are exact replicas in everything but size, of century old specimens as they occur in nature. The Japanese have developed other forms of dish gardening, but to the American horticulturist perhaps none is so interesting as “Bon-sai.” Donald Wyman [ 3-5 ] 1 . H^-’* “ uH. . -5 ir :iv^* “ ■ •'■J’i %y. ' *y- *•*/' i*/ ' . • . * ■ ‘ « * , j • *; i;^, ■ ■*f;.- Tf t4 j ‘ ti ->l i If' if ** i> -f' :.-L. 4"r»V" ■’' • vi{“‘ ■ ■ /■ fcr. .' ^ 'l'-^- ■}: .rl - : . >:V . . vt< - • r. ' ^HfTW r 7 *’ '" w.- --^ ' '-/■^ ^ - ■*'•''■ •^■*' I,.- ', ■<.> '.-!„pi* • V?.. -- .* v' ‘ 'f ■, • ■» a f ;-v *• >' V * ' i .; -\Tr..s ■:; •/ ‘'. '' , H ' \ m ■ .73 i ■’ . fi j)>'^ ..V7; i '■‘ : *. « . ' _ i ■Z\ • K-. •, v:- - ■' ' ^ , ..Iw . .• „ .^1. J A continuation of the Bulletin of Popular Information of the Arnold Arboretum, Harvard University Volume 11 MAY 23, 1951 Number 5 SOME SHRUBS FOR AT LEAST TWO SEASONS OF BEAUTY Many gardeners fail to realize that there are literally several thousand shrubs that are being grown in various parts of the northern part of the United States. Certainly all are not of the best ! There must be some basis on vdiich these plants can be judged in which the better ones might be easily pointed up. I would like to suggest that one basis on which such shrubs can be selected is the number of seasons during which they are of real ornamental value. Take for instance the yews or Ilex crenata convexa or many of the evergreen rhododendrons — these plants are of interest every season of the year because of their evergreen foliage. On the other hand, some of the forsythias, deutzias, spireas and lilacs are only of special interest during the two-week period that they are in bloom. They liave no interesting autumn color, they have no bright colored fruits, they have nothing particularly meritorious for winter display. Of course such plants will always be needed in many gardens, but the important point to emphasize is that in the small garden, where space is at a premium, plants might well be used that have ornamental interest more than one season during the year. The viburnums are excellent examples of plants in this group. These plants have conspicuous flowers in the spring, many of them have bright colored fruits in the fall, some of them lasting all winter long, and most have a rich red to purple-red autumn color. Surely such plants merit first consideration on the small property. A suggested list of some of these good plants is given here together with some specific information as to why they are included. 1 . Flowers 2. Fruit 3. Summer foliage 4. Autumn coloration 5. General form [37] (). Winter t\vi«r or bark 7. Winter fbliajre 'I’lie numbers l)eIo\v refer to the reasons why tliese shrubs are valued for orna- mental use. Abelia <;ran(liriora 1, Aeer palmatum varieties .S, Amelanehier ‘rrandiHora 1, t, (5 Berberis species 1, -2, t, and some 7 Cbionantlius virjjinicus 1, ^2, 4- Cornus alba sibirica 1 , +, (> C. mas 1, 2, 4, .7 Cotinus cotrcrytrria purpureus 2, 4 Cotoneaster dammeri 2, 7 C. horizontalis 1, 2, 5, 7 C. micropbylla 1, 2, 7 C. salicifolia floccosa 2, 7 Cytisus praecox 1 , b C. scoparius 1 , (3 Daphne species 1 , 2 Enkianthus species 1 , 4 Euonymus alata compacta 4, 5 E. fortunei vegeta 2, 3, 5, 7 Eothergilla species 1 , 4 Hamamelis species 1, 4 Hydrangea petiolaris 1, 3, 5, 6 Ilex cornuta 2, 3, 7 I. crenata 2, 3, 7 I. yunnanensis 2, 3, 7 Kalmia latifolia 1, 3, 7 Kolkwitzia amabilis 1, 2, 6 Leucothoe catesbaei 1, 3, 4, 7 Ligustrum obtusifolium regelianum 1 , 2, 3, 5 Lonicera amoena arnoldiana 1, 2, 5 L. bella 1, 2 L. fragrantissima 1, 2, 3, 7 L. korolkowi floribunda 1, 2, 3 L. maacki 1 , 2 L. tatarica 1, 2 Magnolia stellata 1, 2, 3, 4 M. virgin iana 1, 2, 3 Mahonia species 1, 2, 3, 4, 7 Malus sargenti 1, 2, 3 Bbiladelplius floridus 1, 3 E. grand ihorus 1, 3 E. laxus 1 , 3 E. virginalis “Bouquet Blanc,’* 1, 3 E. splendens 1, 3 Eieris species 1 , 3, 3, 7 Erinsepia sinensis 1,2,3 Erunus tomentosa 1, 2 Rhododendron carolinianum 1 , 7 R. catawbiense 1, 7 R. fortunei 1 , 7 R. schlippenbachi 1, 4 R. vaseyi 1 , 4 Rosa helenae 1, 2, 3 R. multiflora 1, 2, 3 R. roxburghi 1, 3, 7 R. rugosa 1, 2, 4 Spiraea prunifolia plena 1 , 4 Taxus baccata 2, 3, 3, 7 T. cuspidata 2, 3, 3, 7 T. media 2, 3, 3, 7 Vaccinium corymbosum 1, 2, 4, 6 Viburnum cassinoides 1, 2, 4 V. dilatatum 1, 2, 4 V. japonicum 1, 2, 3, 7 V. lentago 1, 2, 3, 4 V. opulus 1, 2, 3, 4 prunifolium 1, 2, 3, 4, 3 V. rufidulum 1, 2, 3, 4 V. sargenti flavum 1, 2, 3, 4 V. sieboldi 1, 2, 3, 4, 3 V. tomentosum mariesi 1, 2, 3, 4, 3 V. trilobum 1, 2, 3, 4 [ 38 ] Donald Wyman THK KFFPXT OF LIGHT OX SFFD GERMINATION For many years we have had difficulty in germinating the seeds of certain species of trees even when stratified in the usual manner. If, however, the seeds ■ are left on the surface of the ground under the trees, they germinate readily. (}erminating seeds collected in early spring are planted on moist sphagnum, i where they develop rapidly. The young seedlings are then transferred to pots or Hats. In this way we have been able to get early germination of Cedrus libani, ' Pseudolarix and Acer griseum. The more rapid and complete germination of seeds exposed over winter on the surface of the soil may be related to experiments recently reported by Dr. Risto Sarvas of the Forest Research Institute of Helsinki (Oikos Acta oecologica Scan- : dinavica 1950). Dr. Sarvas finds that the seeds of Picea excelsa, Betula verrucosa,^ Betida pubescens and Pinus sylvestris^ germinate much more rapidly if exposed to \ light. The seeds sown on the surface of the soil, or very lightly covered, germi- nated more rapidly than those kept in the dark or planted deep enough to ex- | elude the light. j If light is a factor in the early germination of seeds exposed on the ground ) under natural conditions, the method of germination developed by Dr. Sarvas f may give equally rapid germination under artificial conditions and without the hazards of exposing seed to rodents during the winter. | Lewis Lipp ARNOLDIA A continuation of the Bulletin of Popular Information of the Arnold Arboretum, Harvard University Volume JUNE 8, 1951 Number 6 smaller street trees needed Times were different one hundred and fifty years ago ! Take street tree plant- ing for instance. Only a very few kinds of trees were used, and the mighty xAmerican Elm was placed at the top of the preferred list. Its great height and lofty arching branches were such that eventually it not only shaded the street completely but also shaded the houses near by as well. During the ensuing cen- tury and a half conditions changed. With the tremendous increase in the popu- lation of the urban centers came a corresponding increase in property values, especially along the street. The space in which trees were allowed to grow form- erly was continually reduced and buildings and paved walks and streets were pushed closer and closer over the wide spreading roots of such giants as the elms. The horses and buggies of our forbears were gradually changed to horseless carriages — motor machines that emitted gases poisonous to plant growth. At first, this was negligible, but as traffic increased these "gases became greater and greater in proportion. This, combined with the fact that the root area allotted to street trees became smaller, did not aid in their perfect growth. Labor costs became greater, and with larger trees of the magnificent size of mature elms, spray costs and pruning costs reached an all time high. Then came the Dutch elm disease, a cruel and unscrupulous killer of trees. It was then that the street tree departments of many a town began to realize the tremendous cost of removal of large specimen trees. When it costs between $100 and $300 to remove a single tree, some of the towns where killing had been es- pecially great, soon found that normal budgets mean little with a large number of trees to be removed annually. It was then that many an individual responsible for planting street trees, began to look around for “substitutes” for the American Elm. Of course, there are no real substitutes, for no tree has the wide arching habit of the xA.merican elm. However, it is becoming increasingly apparent to many [41 ] I) (and the Arnold Arboretum has been preaching this for fifteen .years) that the time has come to carefull.v scrutinize man.v other trees that might be suitable for street tree planting ^ especiall.v trees smaller at mature size than the American Fdm. Modern towns do have overhead power lines, much as we dislike them. In some situations, propert.v owners are fortunate in forcing their placement under- ! ground, but the great cost precludes this in all but the largest and most con- gested urban areas. Wh.v not select some small tree, that will reach its mature heiglit under the power lines? Street Planting While the planting of our major highwa.vs is done chiefl.v b.v highl.v trained state and federal experts and is out of the hands of the average citizen, tree planting along the streets of the towns and cities is much closer to him and he ' ma.v even serve on a “tree selection” committee. Frequentl.v it has to do with planting on his own property. There are a few generalities about this t.vpe of i planting that might be kept in mind. Attempting to grow trees in the heart of our largest cities, is one thing, and | i growing them in the suburban areas of such cities or in the thousands of towns | ; and villages across the country is another. Very few trees will thrive under the | exceedingly tough growing conditions of the city while more might be tried in | areas where more soil-space is available, and where traffic hazards, soot and smoke i are not as severe. In some of the major office buildings recently erected in our large northern ■ cities, trees are ver.v much wanted as ornamental features, but they must resist ! terrific odds in order to survive. The paved walk is all about them and in some ; places heating pipes are put near their roots to be turned on in the winter to j keep the snow melted on the sidewalks above ! About all that can be said of such j planting is that onl.v the most resistant varieties should be selected and the j amount of open ground about their roots should be as much as will be allowed j by the architects. | The minimum amount of open ground for a tree to grow in is a square 8' on a side, the larger the better. Often a space 12'xl2' is provided. In many European cities and in this country as well, widely woven iron grating is placed over this i soil to allow for water to seep through to the roots while at the same time pro- j viding for foot traffic over it without pounding the soil down to such an extent that it bakes almost as hard as concrete when it is dried out. Such a condition ' is not conducive to the free passage of air or rain water to the roots, without which the tree will frequently sicken and die. Much attention should be given the matter of tree planting before the street i is finally laid out by the town engineers. In the horse and buggy days, trees were planted along the street with tree trunks often abutting the curb. Toda.v { with automotive transportation what it is, much more room must be given drivers [42] PLATE XII The Sentry Ginkf^o planted alon^ the Roosevelt Boulevard in Philadelphia, Pennsylvania. The narrow f>rowinf>^ trees eoidd be used alonj^ a street considerably more narrow than this wide boulevard. on tliese streets. If this is not done, accidents (often caused by skidding^) are serious, not only to tlie traffic but to the trees themselves. ! 'file best method of plantingr along: suburban streets is to allow a strip of ground i between the sidewalk and the i)roperty line in which trees are planted. This strip should be a minimum of to 8' and better still if some of the larger i growing types of trees are to be used. This arrangement is ideal, for it does not > encroach on private property, yet affords plenty of space for the future develop- ; merit of the trees. It places the tree away from service lines, pipes and sewers ■ that are frerjuently placed at the edge of the street paving, a decided advantage for when tliese are opened up and tree roots are in the way, they are usually d mercilessly cut. Idiis system is working remarkably well in the newer suburban developments of many large cities, especially in Denver, Colorado, and some areas about Cleveland, Ohio. The property owner can take care of the grass in i this strip, and the town will be responsible for the care of the trees. This type of cooperation between the town and the private property owner is obviously an arrangement only feasible when the street and abutting properties have been laid out with this in mind, and certain ordinances have been approved in order for the arrangement to work successfully. In older suburban areas, where such space is not available, but where the i houses are set back considerably from the property line along the street, trees can be planted on the edge of the private property. The sidewalk may or may not abut the street but even if it does not and there is a small grass strip be- tween the sidewalk and street, no trees would be planted in it. They would ^ instead be planted on private property, particularly if the property line abutted i the sidewalk. This method of tree planting obviously creates several complica- i tions. It would require special town ordinances governing the care and removal of such trees. It would also require the major cooperation and enthusiasm of the original property owners along a certain street. Once the system is agreed on jj and approved, it is seldom that such purchasers of such property already planted with street trees would seriously object. This plan has many good points, especially from the standpoint of the health of the trees. They would be away from the street and its destructive traffic, their major roots would be away from the destructive ditch digging operations fre- : quently encountered and property owners as a rule would take pride in their , general good health. This plan is working in some areas, but it is obvious that it takes considerable cooperation between property owners and town officials. It can result in more beautiful trees and more permanent trees, which both groups ! should obviously desire. In many cities and towns neither one of these methods of tree planting is pos- ' sible and the trees must be planted between the sidewalk and the curb. No tree should ever be planted closer than sV to the curb, and the further away it is, the better for the tree and the passing traffic. The ideal width for this strip of [u] grass between curb and sidewalk would be and the tree would not be centered in it but planted closer to the sidewalk than the street. Street trees should not be planted opposite each other but should alternate, allowing for a greater development of the tops. Spacing should be at least 75' apart. Planting closer than this (e.xcept in the use of very small tree species) only creates more costlj’ maintenance, and sometimes may necessitate the re- moval of some trees which are crowding others. It is far better to plant fewer trees and take care of them properly, allowing them plenty of room for develop- ment, than to crowd them close together in order to make a “show” while they are young, at the same time greatly increasing their maintenance cost. Size of Tree at Planting Time It is being found by many whose responsibility it is to plant trees along the town and city streets of the country, that smaller trees are much better to use in general street planting — smaller in size at the start and smaller in permanent stature. Trees with a mature height of under 40' can be far less costly to remove. The landscape effects of the tall tree and the smaller tree may not be the same, but there is a nation-wide trend now to consider using smaller trees along the streets of our cities and towns. Admittedly the need for medium or tall trees will vary with circumstances and specific situations. Also, it is far easier to plant several trees l" in diameter, than one 4" in diam- eter. The smaller trees are more easily acclimated to the new situation, and if properly root pruned and top pruned in the nursery will grow even better the first two years than the larger tree. Water can be added to better advantage, more of the right soil can be given at the start, so the smaller tree usually starts in a more vigorous growing condition than does the larger tree. This bears some thought. Smaller trees are more easily broken and admittedly there are always places where larger trees must be planted. The arborists of the country have the information and the equipment to move trees at every time of year. There will always be a demand for big tree moving by these experts. However, -in the cramped, tough situations in which most street trees are required to start growth, trees of an inch caliper or slightly more usually will get off to a better start than trees of larger caliper. The cost in trans- planting is also considerably less. Consequently, the tree superintendent can concentrate on a comparatively deeper hole, on better soil and give more atten- tion to water requirements of the new smaller tree. With mounting labor and transportation costs, these two points are going to prove very important in street tree planting programs during the immediate future. Some towns like Brookline, Massachusetts, have a policy whereby small streets are planted with one type of tree only. The governing shade tree commissioners see to it that many different types are used throughout the city. It is not with- [-^5] PLATE XIII Crataegus monogyna iuermls, a thornless hawthorn with a dense rounded head. j 1 out reason to expect that the majority of property owners on one street might decide on the Sargent Cherry, for instance, whereas on another street another majority would request the Littleleaf European Linden. An intelligent shade tree commission, with certain standard policies, and always ready with helpful suggestions in such cases, could easih’ mold a most interesting over-all tree plant- ing program that would go a long way to make the town beautiful and interesting. Small Trees Height 7.one ^Acer argutum ^24-' A. campestre 25' A. circinatum 25' A. cissifolium 30' *A. carpinifolium 30' A. ginnala 20' A. griseum 25' A. mandshuricum 30' A. platanoides globosum 50' A. spicatum 25' A. tataricum 30' Carpinus betulus fastigiata 30' *Carpinus caroliniana pyramidalis 40' *C. cordata 45' C. japonica 45' *C. turczaniovi 1 5' *Celtis bungeana 45' Chionanthus virginicus 30' Cornus florida 40' C. kousa 21' Crataegus species 20-3.- *C. monogyna inermis 30' C. “ stricta 30' *C. phaenopyrum fastigiata 30' Evodia danielli 25' Fagus sylvatica fastigiata 40' Gleditsia triacanthos elegantissima 35' Koelreuteria paniculata 30' Magnolia stellata 20' Oxydendrum arboreum 30-7.' Fhellodendron amurense 45' *Prunus nipponica 18' *P. sargenti columnaris 35' [-17 4 Hedge Maple 5 Vine Maple 5 5 Hornbeam Maple 2 Amur Maple 5 Paperbark Maple 4 Manchurian Maple 3 Globe Norway Maple 2 Mountain Maple 4 Tatarian Maple 5 Pyramid European Hornbeam 2 Pyramid American Hornbeam 5 Heartleaf Hornbeam 4 Japanese Hornbeam 5 5 Bunch Hackberry 4 Fringetree 4 Flowering Dogwood 5 Japanese Dogwood ' 3-5 Hawthorns 4 Thornless Single Seed Hawthorn 4 Upright Single Seed Hawthorn 4 Pyramidal Washington Hawthorn 5 Korean Evodia 4 Dawyck Beech 4 Bushy Honeylocust 5 Golden-rain tree 5 . Star Magnolia ' 4 Sour wood 3 Amur Cork Tree 5 Nipponese Cherrj’ 4 Columnar Sargent Cherry ] Mh’unus serrula SO' 5 P. serrulata var. 20-25 ' 5- 0 Oriental Cherry 'kobinia pseudoacacia umbraculifei ra 35' S Umbrella Black Locust Syringa amurensis japonica 30' o Japanese Tree Lilac ■Ulmus carpinifolia umbraculifera 35' 4 Globe Smooth Leaved Elm \'iburnum lentago 30' o Nannyberry W prunifolium 15' S Blackhaw y. rufidulum SO' 5 Southern Blackhaw y. sieboldi SO' 4 Siebold Viburnum Narrow Trees for Narrow Streets (Not necessarily low in height) Acer platanoides columnare 75' S A . ^ ^ erectum 7 5' S Erect Norway Maple A. rubrum columnare 75' s Columnar Red Maple Ginkgo biloba fastigiata 50' 4 Sentry Ginkgo Quercus robur fastigiata 50' 5 Pyramidal English Oak Tilia platyphyllos fastigiata 50' 3 Columnar Big Leaf Linden Ulmus americana ascendens 100' 2 U. columnaris 100' 2 Columnar American Elm U. * ** ‘‘Augustine” 100' 2 'U. carpinifolia cornubiensis 50' 4 Cornish Elm U. “ dampieri 50' 4 Dampier Elm 'U. “ koopmanni S5' 4 Koopmann Elm U. “ sarniensis 50' 4 Jersey Elm U. glabra exoniensis 50' 4 Exeter Elm U. hollandica belgica 75' 4 Belgian Elm U. “ “Klemmeri” 50' 4 'U. “ superba 75' 4 Blanford Elm * These are apparently not yet offered by American nurserymen but plants are growing in this country and there is no reason why stock could not be worked up. As for the others, they may not all be available in sufficient numbers or the proper sizes to meet the increasing demand but there is no reason M’hy their production should not be increased. And these are not all the possibilities, but certainly enough to initiate the idea that smaller trees are growing in this coun- try and it is high time they are propagated commercially and planted along our streets. Donald Wyman [48] ARNOLDIA A continuation of the Buixetin of Popular Information of the Arnold Arboretum, Harvard University Volume 1 1 OCTOBER 26, 1951 Numbers 7-8 AIR LAYERING WITH POLYTHENE FILM The making of air layers on woody plants to induce rooting is a practice that is centuries old. Generations of Chinese did it, and undoubtedly it was in- troduced into America by the earlier settlers. Until comparatively recently, the method has been used chiefly in the greenhouse. It consisted of scarifying the stem of a plant and wrapping moist moss (or soil) around that injured plant part. If the wrapping material was kept moist continually, rooting often occurred. The difficult}’ came in keeping the wrapping material moist. Rubber or paper wrap- pings did not prove satisfactory, and watering of the wrapping would frequently have to be done daily and even several times a day in a hot greenhouse. This continual care was frequently more bother than it was worth. In 194-7, Colonel William R. Grove of Laurel, Florida, found that the old- fashioned method of air layering could be decidedly augmented with the use of ; one of the newer plastic films. He published his findings dealing with the propa- gation of Lychee in the 194-7 “Proceedings of the Florida Horticultural Society.” , Colonel Grove at first used “Pliofilm” manuffictured by the Goodyear Tire and ! Rubber Company, Inc., but he found that it disintegrated before the roots formed. Then he used “Vitafilm” this yielding much better results. On the i strength of this he has used it (and other materials as well) in commercial prop- { agation, and applied for a patent, granted four years later, covering use of plas- i tic material in air layering process.* I In 1950 John L. Creech of the United States Department of Agriculture Sta- I tion at Glenn Dale, Maryland used plastic films with good success in the propaga- I tion of evergreen rhododendron air layers, and published some of his experiences in the National Horticultural Magazine, July 1950. He used a polythene film successfully. The Arnold Arboretum, after suggestions made by Mr. Creech , earlier in the year, started using polythene film around air layers in the summer j * Airwrap Products, Box 142, Sarasota, Florida. :i of 191-9. Results proved so interestinjr that additional experiments were tried in 19.)(), some plants showinir rooting that might not ordinarily be expected to root as cuttings. During the past summer, Mr. Heman Howard of the Arnold Arbo- retum placed air layers on species and varieties of woody plants. Some were placed early in the spring, some were placed on the current year’s growth in June and July, in an attempt to determine whether this is a reliable method of rooting difficult plants. The results this year have been rather disappointing in that many of the air layers failed to root. Even with the failures, there remain : enough possibilities to make this method of interest for everyone, and in order to place some of this information before ARNOLDIA readers the results accom- ; plished in some of these experiments are recorded here. i Polythene Film I* 'rhere are a confusing number of plastic films now on the market, and all do not have the same properties. The important properties of the film necessary for assisting in the proper rooting of air layers, would obviously include high per- meability to gases like oxygen and carbon dioxide, and a very low permeability to water vapor. A few years ago the Imperial Chemical Industries Ltd. of England developed a plastic known as ‘^Polythene,” a high polymer of ethylene. E. I. DuPont de Nemours & Company was licensed to manufacture this resin in the United States in 1943. Originally DuPont used the name ^^Polythene, ” but later adopted the trade name ‘\\lathon” for this new plastic. Bakelite Corporation is also licensed to manufacture this resin, they calling their product “Polj^ethylene. ” These new plastic films are now widely used for packaging foodstuffs under such trade names as ‘^Howard-Seal,” ‘‘Pearlon,” ‘‘Tralon,” “Visqueen,” etc. Specificall^v, the material used at the Arnold Arboretum was one of these, purchased from the Harwid Company of Cambridge, Massachusetts under their trade name of * Dura- Clear,” manufactured from the resin ‘*Alathon.” It is unfortunate that the terms Polythene” and ^ * Polyethylene” have both been used as the generic name for the high polymers of ethylene since they are confusing to the layman. The point is, that the Dura-Clear” used in our experiments, has the same properties as the ‘^\lathon” of the DuPont Company. These properties are as follows : Thickness of Film 0.001" 0.002" 0.003" 0.004" 0.006" 0.008" Transjjiission of H ater Vapor (in grams per 100 sq. inches of exposed film surface during 24 hours) 0.93 0.63 0.46 0.32 0.21 0.13 [ ->0 ] Permeability to Gases Gasex Oxyoen Carbon dioxide Xitrofjen Hydrogen PermeahUifij in cubic ceniimefers per 100 sq inches in 2 If. hours 1 7 o 700 (higher if water vapor is present) 7^2 ^225 The thickness of the “Dura-Clear** film we used was four thousandths of an inch, but thinner material would probably have served just as well. It is these qualities relating to water vapor and permeability to certain gases that make this material ideal when wrapped about air layers. (The same properties and its trans- parency make it ideal in packaging perishable fruits and vegetables.) It is obvious, from the above, that the polythene film should be conducive to rooting. It should be noted that air layers have been kept perfectly moist by this film, when the wrapping of the film is done tightly, for periods of up to one year in length. Sometimes the sphagnum moss in the wrap actually grows, and grass seeds germinate and grow vigorously when included in the moss mixture. Because the film is fairly transparent, the rooting of the twig inside can some- times be noted without even opening the wrapping. This polythene film (the term used here to include all such trade-named pro- ducts as mentioned on page .50) is ideal for ])ackaging plants also. Mr. Richard Fillmore, the Propagator at the Arnold Arboretum, has merely wrapped dormant scions of roses in polythene with very little sphagnum moss, sent them by ordi- nary mail to England where they arrived five weeks later in perfect condition. He also wrapped scions of roses {Rosa hugonis) without packing material and placed them in the refrigerator for about 12 months with no bad effects, after which they were grafted and some grew successfully. Some azalea plants {?>' tall) were dug last spring at the Case Fistates, the roots washed free of all soil and then wrapped tightly in polythene film. Some were kept outside, others were kept at room temperatures for a full month, then were planted out, and all grew normally thereafter. The Air Layer The making of the air layer itself is very simple and the principle is over a thousand years old. A longitudinal cut of about two inches upward is made on the young twig, the cut going nearly to the center of the twig. (An adaptation of this is to remove a complete circle of bark one half inch wide around the stem.) Then both cut surfaces are dusted with some hormone rooting powder which may (or may not) aid in the rooting. We have used Hormodin but undoubtedly other materials are just as good. Moist sphagnum moss — about a handful — is packed beiiceen the cut surfaces and then all around the entire cut, fully covering it. Polythene film is wrapped carefully and tightly about it, then tied top and bottom. [51 ] l{iil)l)er bands used in jrraftinjr liave not proved satisfactory for tying. Mr. James M . Rooney of Attleboro, Massachusetts, suggested the use of Scotch Klectrical 'I’apc and this has proved most satisfactory. 'I'lie \vrai)i)ing and tying of the film should be done in such a way that the moss is well contained and that no opening in the film is left for the evaporation of the moisture from the moss. Mr. Fillmore has pointed out that the overlap of the film wrapjnng should be on the underside of the air layer so rain water will not seep in. Also he has pointed out the very important fact that in taping the top end of the wrap the tape should be started on the bare twig and gradually spiral down to completely close the top end of the wrap in order that rain water will not seep down the twig and into the moss inside. In Plate XIII this is not done i)roperly. Many of the air layers we made in 19.31 may have failed to root because this was not done, water seeped into the moss packing, pushing out much of the air and creating a soggy condition decidedly unfavorable to rooting. If properly done, the air layer will remain moist for months (we have had some remain moist for a year) and rooting may take place in a few months’ time. This is all there is to the operation. The time it is done, the size of twig used, the amount of hormone powder used and the amount of moisture in the moss are variables with which one has to contend for proper rooting. We have placed air layers in early spring on wood that is dormant, and again in June and July on twigs that grew the current year. As far as our results have been concerned, there seems to be a considerable variation and one would expect that rooting might easily vary with the species. Many plants are propagated from both *^hard wood” or dormant cuttings, and soft wood” cuttings made of wood grown the current year; others may root better from one or the other type of cutting. Con- secpiently one would expect the time these layers are applied might well vary with the species, for best rooting. Twigs have been rooted that were a half inch in diameter, although usually one might expect normal rooting from the twigs about the size of a lead pencil. We have undoubtedl.v been over-generous with our applications of the rooting powders, and Mr. Fillmore has suggested that, from the appearances of some of the layers later, too much has been applied, for some have shown what appears to be hormone injury. This also is something what will have to be worked out later. Because so very little moisture passes through the film, one should be ex- tremely careful not to have too much moisture in the sphagnum moss at the time it is applied about the cut. The moss should be scpieezed prior to application, so it will be moist — not wet. [ ] SCOTCH PLATE XIII. Materials used in air layer experiments at the Arnold Arboretum. Note comments on making? a proper seal at the top of the layer, paj^e 52. Plants which Rooted by Air Layering Number Tried Number Rooted ’’'Abeliopliyllum disticlium 1 1 4 2 Acer barbi nerve 6 4 ‘‘ callipes 3 2 eircinatiim 5 8 cissifoliiim 1 1 diiretti 8 1 ginnala o 1 griseum 8 1 ( ( i ( 8 1 grosser! hessi 4 8 palmatum dissectum 4 I ‘‘ pensylvanicum 6 6 * platanoides 6 4 i 4 6 6 4 1 globosum 6 6 6 6, 4 8 nanum 2 2 6 6 6 6 var. 4 4 ^ ‘ saccharum monumentale 8 1 Aesculus carnea 4 2 hippocastanum 6 2 “ umbraculifera 4 1 *Albizzia julibrissin rosea 10 5 Betula aurata 8 1 ‘‘ fontinalis 4 2 Carya tomentosa 6 1 Castanea mollissima 10 1 Catalpa bignonioides 4 4 bungei 4 I speeiosa 4 2 Cercis chinensis 4 2 Cladrastis platycarpa 8 2 Clethra barbinervis 8 2 *Cornns alba sibirica 8 8 Cornus florida rubra 9 8 Corylopsis glabrescens 4 8 spicata 4 8 Corylus chinensis 4 1 ^Liiyers made in 1950, a 11 others in [54] 1951. Plants which Rooted by Air Layering (Cont.) Xi/mber Tried Xurnber Rooted ‘Cotinus coggygria purpureus 4 4 a a a 1 1 3 Cotoneaster foveolata 4 4 “ horizontalis 4 4 Crataegus monogyna stricta 6 1 “ pinnatifida major 6 1 Cytisus praecox 4 1 “ supinus 4 4 Davidia involucrata vilmorini 1.5 5 Diospyros lotus 4 <2 Enkianthus campanulatus 5 3 'Forsythia “Arnold Dwarf” 3 3 Franklinia alatamaha 4 4 Ginkgo biloba 1 1 Halesia Carolina 6 6 “ monticola rosea 4 4 Hedera helix baltica 4 4 ^Hibiscus syriacus rosea 1 1 Hippophae rhamnoides 6 3 Ilex crenata convexa 4 4 ‘ ‘ glabra 6 6 “ montana macropoda 1 1 “ verticillata 3 1 Indigofera amblyantha 4 3 Koelreuteria paniculata 8 3 Laburnum anagyroides 4 3 “ watereri 8 4 '^Ligustrum ibota aureum 3 3 “ ovalifolium 4 4 “ vulgare buxifolium 4 4 Lonicera maacki 4 2 Maackia amurensis 4 4 Magnolia denudata 10 1 “ soulangeana “ Alexandrina” 4 1 Malus astracanica 4 1 “ atrosanguinea .5 4 “ “Dorothea” 5 5 “ floribunda 6 1 halliana spontanea 5 1 [ -5.5 ] Plants which Rooted by Air Layering (Cont.) Number Tried Number Rooted Mains ‘^Mclntoslr’ 3 2 “ niicromalus 7 <2 “ pruni folia rinki 6 3 ‘‘ purpurea 4 3 “ sargenti rosea t) 3 spectabilis 6 5 sublobata 6 6 “ “Wabiskaw^’ 4 2 Moms alba pendula 4 2 Orixa japonica 4 4 Osmaronia cerasiformis 4 2 ^Fopulus alba nivea 0 2 Prunus juddi 1 1 ‘‘ maacki 2 2 serrulata ‘‘Amanogawa” 4 3 ( ( i i i i ^ , • • Civoiko 2 1 “ “ “ ? ? Kwanzan 6 <2 yedoensis ^ ^Taizanfukun” 4 4 Ptelea trifoliata aurea 6 2 Mlhododendron ‘*Dr. Charles Baumann” 7 5 ^ ‘Josephine Klinger” 9 8 Salix caprea 7 7 Styrax japonica 7 2 Symplocos paniculata 6 3 Syringa amurensis japonica 6 1 prestoniae “Lucetta” 4 3 “ “ “Paulina” .5 3 “ villosa 5 3 ^ ‘ vulgaris vars. 35 9 Tamarix pentandra 2 2 Taxus cuspidata nana 3 1 Tilia cordata 5 3 “ platyphyllos fastigiata 8 2 Tsuga canadensis 3 3 Ldmus carpinifolia koopmanni 6 6 6 6 . . 6 1 sarniensis 4 1 glabra 4 1 Vaccinium corymbosum “jerse.v” 3 2 Viburnum carlesi 4 1 [56] Plants which Rooted by Air Layering (Cont.) '‘A'iburnum dilatatum “ juddi opulus rhytidophyllum rufidulum * ‘‘ sargenti 6 6 6 ( 6 6 Wisteria i ( i < < ( i < ( ( flavum setigerum aurantiacum sieboldi floribunda violacea-plena longissima alba “ ‘‘Xaga Xoda” formosa macrostachya sinensis “ “ hybrid “ venusta Zelkova serrata ‘ ‘ sinica Number Tried 4 4 9 4 b 6 3 4 8 4 4 4 4 4 4 15 2 3 6 6 Number Booted 2 1 1 5 3 4 3 1 2 2 4 2 4 1 2 1 6 3 Plants which Failed to Root Number qf Layers Tried Abies homolepis umbellata 6 Acer campstre b “ palmatum atropurpureum 1 “ “ lutescens 2 “ platanoides b shirasawanum 3 ‘ ‘ tataricum b Aesculus carnea plantierensis 5 discolor mollis 4 glabra leucodermis 4 Albizzia julibrissin rosea lb Amelanchier canadensis 2 Amelasorbus jacki 4 Betula jacquemontiana 3 Carpinus cordata 4 orientalis 4 [57] Plants which Failed to Root (Cont.) Carya glabra ** laneyi ‘ ‘ i. ovata “ sell neck i Castanea dentata Catalpa fargesi Cereis canadensis alba Cliaenomeles sinensis Cliionanthus retusa “ virginicus Cladrastis lutea Cornus florida mas elegantissima ‘‘ officinalis Corylus avellana fusco-rubra “ ‘ ^ contorta colli rna Cotinus americanus Crataegus arnoldiana “ coccinioides “ lavallei “ monogyna inermis a a . f versicolor nitida pruinosa punctata ‘‘ succulenta Diospyros virginiana Eucommia ulmoides PLvodia danielli Fagus grandifolia sylvatica atropunicea pendula Fothergilla monticola Fraxinus chinensis pennsylvanicum Gleditsia triacantlios inermis Hamamelis mollis Number qf Layers Tried 6 4. 4 4 6 8 4 4 2 4 4 8 4 4 8 5 5 4 6 4 2 3 5 6 6 3 4 4 4 2 3 4 2 6 4 6 4 8 [58] Plants which Failed to Root (Cont.) *Hamamelis mollis Juglans cinerea “ nigra ^ (4 4 4 laciniata 4 4 4 4 4 4 Kalmia latifolia “ “ polypetala Kalopanax pictus Lindera benzoin Magnolia fraseri ‘ * loebneri * stellata rosea ( ( ' a a * * * virginiana Malus “Arrow” ‘ ‘ baccata “ “Bob White” “ brevipes “ coronaria charlottae “ florentina “ glabrata “ hupehensis “ . ioensis plena robusta “ sargenti Parrotia persica Phellodendron amurense chinensis “ saehalinensis Photinia villosa Pinus bungeana Primus maritima “Eastham” “ “ “Raribank” serrula Pseudolarix amabilis Quercus bebbiana bicolor dentata * Layers made in 1950, all others in 1951. [ 59 ] y umber of Layers Tried 3 6 9 4 ,5 5 / 4 3 6 6 4 6 4 3 5 4 1 3 5 4 5 1 4 6 4 9 4 6 4 5 4 4 5 4 4 6 4 PLATE XIV wShowing' the rooting of Malus “Dorothea" in September 1950, three months after the air layer was made. Plants which Failed to Root (Cont.) Xumher of Laijer.s Tried Quercus falcata marilandica “ monjjolica robur “ ‘ ar<^enteo marginata ^ runcinata “ stellata variabilis Rhododendron “Mrs. C. S. Sargent'* “ “Purpureum grand iflorum” “ ‘ Watereri*’ Robinia longiloba Sophora japonica Sorbus alnifolia “ aria “ aucuparia “ latifolia “ matsumarana pratti thuringiaca Syringa pubescens Taxus cuspidata expansa Thuja standishi Tilia americana fastigiata “ platyphyllos Tsuga earoliniana L’lmus carpinifolia dampieri “ “ uinbraculifera “ “ wredi “ j)lotti Vaccinium corymbosum “Harding*’ Wisteria ‘ Jako” 3 o 5 6 4 6 .3 4 4 o .3 3 4 4 4 8 6 4 3 4 4 4 .3 4 4 b 4 6 4 4 o o Results It will be noted from the results that only a few plants were tried that are easy to root from cuttings. The process was merely checked at first to ascertain whether easily rooting plants like Forsythia, Idgustrum, Syri/iga prestoniae. Pop- ulus, the Siberian Dogwood, Tamarix and some of the Viburnums would root this way as well. Although the other materials (listed as rooted) may be rooted from [ (',1 ] cuttinj^s, most can be considered as “difficult” wlien handled in this way. The purpose of these reported experiments was to ascertain which of these difficult- to-root plants, would respond to tlie air layer technique, possibly saving a time- consuming grafting operation. It must he admitted that after the roots are formed, the matter of cutting the potential plant from the parent is not simple. Only a few attempts were made to pot these plants. Mr. Lewis Lipp rooted twigs of the McIntosh apple, but was unsuccessful in getting the plants to grow after they were potted. Some of the other plants are in the same group. It may well be that cutting the rooted twig from the parent plant should best be done at a certain time, or gradually, or that the moss in the air layer might be taken from it and soil substituted before the plant is cut off. These first experiments have to do only with the formation of visible roots during one growing season. Most of the layers were put on either in late April or July 1951 and were re- moved in early October. The majority of those that did not root were well cal- lused, some much more so than others. Air layers that were opened by vandals, that broke off in high winds, or that died because of improper cuts, do not enter into the figures given. This age-old subject of air layering now appears to be given a great impetus due to the properties of these new plastic films. If these results can be repeated, the percentage of rooting increased, and the young plants removed from the parent satisfactorily, this method of propagation will be a highly valued one in any garden where rare and difficult-to-propagate plants are grown. Donald Wyman [ li-i ] ARNOLDIA V • — ♦ — ^ '^KD UNIV^!^ A continuation of the Bulletin of Popular Information of the Arnold Arboretum, Harvard University Volume 11 NOVP^MBER 9, 1951 Number 9 SIMPLE KEY TO THE PINES (Native or available from nurseries in the United States) This simple key is offered chiefly for the benefit of the amateur gardener who is frequently confronted with keys which he finds unnecessarily complicated. The key is based primarily on foliage characters which, in most cases, can be ob- served without the use of a hand lens. It should be clearly understood that any key based primarily on the length of the leaves (and this key is just that) isopen to serious criticism because tlie length of the leaves of any plant will vary with the individual as well as with soil, age and climate variations, disease infestations and altitude at which the tree is growing. Other plant characters vary likewise. However, in order to assist the gardener who has an interest in pines, this key is offered in spite of just such criticism. It includes only those pines which one is likely to find in the woods or nurseries of this country. A few native species have been omitted because they occur only in limited areas, and many exotic species are omitted because they have not yet been widely distributed in culti- vation. It goes without saying that the more species included in a key, the more complicated that key becomes. There are about 80 species of pines distributed throughout the northern hemi- sphere, 27 of which are growing in the Arnold Arboretum. This key includes all but four of the species native to the United States, as well as 15 exotic ones avail- able from nurseries, all in all, 38 species of pines. All measures of leaf length should be considered as approximate only. On one individual tree needles may vary in length from 2 inches to as much as 8 inches, but in the key the length given would be 4 to 6 inches, meaning that mature needles — not' the young ones which are elongating, nor the ones on weak or on over-vigorous branches — are mostly within the 4 to 6 inch length. If this is clearly understood by those using this key, the key will undoubtedly prove help- ful in the identification of most of our commonly grown pines. 'File key is designed to be used cliiefiy with liviiiir material, hence the color of ■ the foliafre and the ‘jeneral habit of the tree sometimes plays an important part. * Occasionally, as in differentiatinjr between P'nnts strohus and P. iiionticola, the two ; species are so much alike that cone characters are used , but these are resorted to • oidy when absolutely necessary, for many a tree which one would like to iden- tify is not jrraced with cones at the time one wishes to identify it. 'rids key can be jrreatly simplified for there are not many pines which are com- monly found in any one area in the United States. As an example, let us con- sider the five-needled pines. 'J'here are at least 15 five-needled pine species of which 1 1 are <;rowin‘? in the Arnold Arboretum, 'rhirteen species and 3 varieties are listed in the following: key. If this key were desif^ned merely to identify the five-needled pines native to this country, the list would be reduced to 7 species. : If the key were to be used in identifying the five-needled pines native in the ' northeastern United States only, this part dealing with five-needled pines would : include merely P. strohus. Hardiness is given according to Zones in the Hardiness Map published in for- mer issues of Anioldia (Vol. 3, \o. 10, p. 53, 194-3). Habitats are also given, because sometimes such information may prove helpful in assisting in plant identification. There is no excuse for avoiding a simple kej’ such as this one, merely because of a lack of thorough botanical training. Such keys, when carefully made, are understandable, and if they are used with a full knowledge of their limitations, they will prove most helpful to the gardening public. Identifications made by the use of any key, and this one in particular, should not be considered final, but should be further checked against a complete description in some standard text, | and available illustrations. ^ SIMPLE KEY TO THE PINES I Native or available in North America Needles in bundles of ^ to 5, rarely solitary, enclosed at the base bj’ a decidu- ous or persistent sheath ...... Pinus Needles 5 in a sheath alhicaulis — White Bark Pine aristata — Bristle-cone Pine cemhra — Swiss Stone Pine fle.vilis — -Limber Pine griffithi — Himalayan Pine koraiensis — Korean Pine lamheri'iana — Sugar Pine mouticoJa — Western White Pine parviflora — Japanese White Pine parviflora glauca peuce — Balkan Pine pumila — Japanese Stone Pine strohus — Eastern White Pine strohus fastigiata strohus uaua torreyana — I'orrey Pine ^2. Needles usually less than inches long with smooth margin P. aristata (California to Colorado) Zone 5 2. Needles usuallv l-r to 2 inches Ions' S. Bark of trunk brown to creamy white, needles rigid and stout, margin smooth ....... P. albicaulis (British Columbia to California) Zone S 3. Bark of trunk black, needles more flexible d. Needles bluish green, often twisted, intensely white underneath, leaf margin finely serrulate, i.e., rough to the touch . P. parviflora (Japan) Zone 5 d. Needles intensely bluish green . . P. parviflora glauca d. Needles light green, not twisted 5. Mature twigs glabrous, needles smooth . . P. flexilis (Alberta to California) Zone d 5. Mature twigs pubescent; leaf margin finely serrulate, i.e., rough to the touch ...... P. pumila (Japan) Zone 3 2. Needles mostly 2^ to d|^ inches long; leaf margin serrulate, i.e., rough to the toueh ^ 3. Mature twigs glabrous d. Plant shrubby, not tree-like ... P. strobus nana d. Branches upright, tree dense 5. Needles stiff . . . . . . . P. peuce (Balkan Mts.) Zone d 5. Needles soft and flexible . . . P. strobus fastigiata d. Branches horizontal, tree more open 5. Cones usually 2 to dj inches long; twigs glabrous or only slightly pubescent ...... P. strobus (Eastern U.S. and Canada) Zone 3 5. Cones usually d^ to 10 inches long; twigs pubeseent when young (British Columbia to Idaho and California) Zone 5 P. monticola (These two species are difficult to tell apart with the naked eye, except that the habit of P. monticola is more narrow and dense and the needles stiffer than are those of P. strobus.) 3. Mature twigs pubescent d. Tree densely upright, pyramidal in habit (Alps of Europe) Zone d d. Tree not as above, more open P. cembra 5. Needles lustrous, dark green (Jajian, Korea) Zone 3 3. Needles dull green P. koraiensis 6. Terminal bud blunt almost globular, eones 12 to 20 inches (Oregon to California) Zone 5 P. lambertiana 6. Terminal bud sharply pointed, definitely not globular, eones d to 10 inches ...... P. monticola (British Columbia to Idaho and California) Zone a [ ] 1. ‘■Z. Needles 4^ to 8 Indies lonjr . . . . P. griffithi (Himalayas) Zone 5 Z. Needles 8 to Pi inches long . . . . P. torreyana (Southwestern California) Zone 9 Needles 3 to 4 only occasionally 5; leaf margin smooth P. cembroides parryana (California) Zone 9 Parry Pinyon Pine Needles 3 in a sheath pomlerosa — Ponderosa Pine radial a — Monterey Pine rigida — Pitch Pine sabiniana — Digger Pine taeda — Loblolly Pine allenuala — Knob-cone Pine buugeana — Lace-bark Pine ca na ri e ttsis — Ca nary Pine coidteri — Coulter Pine jeffreyi — Jeffrey Pine paliistris — Longleaf Pine Z. Needles mostly Z to 3 inches long 3. Leaf sheaths deciduous, bark of older twigs smooth, bark of trunk flaky with white or yellow patches . . . P. bungeana (China) Zone 4 3. Leaf sheaths not deciduous, bark of older twigs very rough, bark of trunk dark brown to black 4. Foliage dark green, cones usually 2 to 4 inches long P. rigida (Eastern U.S. and Canada) Zone 4 4. Foliage bright or bluish green; cones 3 to 7 inches long o. Bark on upper part of trunk and branches smooth P. attenuata (Oregon to California) Zone 8 5. Bark on upper part of trunk and branches rough P. radiata (Southern California) Zone 8 2. Needles mostly 5 to 10 inches long 3. Winter buds resinous 4. Twigs fragrant when broken; cones 3 to 6 inches; foliage dark green, branchlets orange brown . . . . P. ponderosa (Eastern and Central U.S.) Zone 5 4. Twigs not fragrant when broken; cones 9 to 14 inches; foliage bluish green ....... P. coulteri (California) Zone 8 3. Winter buds not resinous 4. Foliage bluish green 5. Needles stout, bark cinnamon red, cones 6 to 12 inches P* jeffreyi (Oregon and California) Zone 3 5. Needles slim, bark red brown, cones 3 to 6 inches P. taeda (New Jersey to Florida and Texas) Zone 6 [GC] PLATE XV 1. Foliage dark green; cones 5 to 12 inches . . P. coulteri (California) Zone 8 2. Needles 8 to 1 8 inches long 8. Foliage gray bluish green 4. Needles slender, drooping . . . . P. sabiniana (California) Zone (5 4. Needles stiff, erect ..... P. coulteri (California) Zone 8 3. Foliage green 4. Needles mostly 8 to 10 inches long, light green and lustrous (Canary Islands) Zone 10 P. canariensis 4. Needles mostly 12 inches or more long, dark green P. palustris (Southeastern U.S.) Zone 7 1 . Needles 3 and 2 in a sheath carihaea — Slash Pine cemhroides — Mexican Pinyon Pine echinata — Shortleaf Pine ponderosa scopidorum — Rocky Mountain Ponderosa Pine tahidaefoi'mis — Chinese Pine 2. Needles less than 2 inches long . . . . P. cemhroides (Southern California and Arizona) Zone 9 2. Needles more than 2 inches long 3. One year twigs greenish to purplish, covered with glaucous bloom (Eastern U.S.) Zone 5 P. echinata 3. One year twigs yellow brown to brownish 4. Terminal bud very resinous . . P. ponderosa scopulorum (Rocky Mountain Region) Zone 4 4. Terminal bud not resinous or only slightly so 5. Needles 2 to 7 inches long; cones l|^ to 2 inches long (China) Zone 5 P. tubulaeformis 5. Needles 8 to 1 2 inches long ; cones 3 to 6^ inches long P. caribaea (Southeastern U.S., Bahamas, ITonduras) Zone 8 ] . Needles 2 in a sheath hanksiana — Jack Pine deusiflora — Japanese Red Pine densiflora ocul us-dracoiiis densijiora umhracidifera echinata — Shortleaf Pine mugo — Swiss Mountain Pine mu go compact a mugo pumilio Needles ^ to 3 inches long nigra austriaca — Austrian Pine pinaster — Cluster Pine pungens — Table Mountain Pine resinosa — Red Pine si/lvestris — Scotch Pine tabulaeformis — Chinese Pine thunbergi — Japanese Black Pine Virginia na — Virginia Pine [ S. Foliage with each needle marked with a yellow band P. densiflora oculus-draconis 3. Foliage bluish green, bark of upper trunk red P. sylvestris and vars, (Europe) Zone 2 3. Foliage green 4. Plant usually shrubby, with several main branches from the base . 5. Needles 5 to 2 inches long, bark black . P. mugo and vars. (Central Europe) Zone 2 6. Dense almost globose shape . . P. mugo compacta b. Shrubby, upright habit ... P. mugo pumilio .5. Needles 3 to 5 inches, bark red to reddish P. densiflora umbraculifera 4. Plant a tree with a central leader 5. Needles mostly 1 inch long . . . P. banksiana (Northeastern L . S. and Eastern Canada) Zone 2 5. Needles to 3 inches long 6. Branchlets usually with glaucous bloom, often greenish to purplish or yellowish 7. Foliage bluish green, cones usually not persistent, bark of up- per trunk red ; leaves flexible . . P. densiflora (Japan) Zone 4 7. Foliage bright green, cones persistent, bark of upper trunk black ; leaves stiff . . . . P. virginiana (Eastern U.S.) Zone 4 6. Branchlets without glaucous bloom, orange to yellow 7. Vigorous shoots often with more than one whorl of branches on the current year’s growth . . . P. pungens (Southeastern C.S.) Zone 5 7. Vigorous shoots with onl}’ one whorl of branches on the current year’s growth 8. Winter buds white or whitish to light yellow P. thunbergi (Japan) Zone 4 8. Winter buds dark brown . . P. tabulaeformis (China) Zone 5 2. Needles 3 to 8 inches long 3. Winter buds resinous 4. Needles slender and flexible, breaking when bent P. resinosa (Northeastern U.S. and FLastern Canada) Zone 2 4. Needles stout and stiff, not breaking when bent P. nigra austriaca (Central Europe) Zone 4 3. Winter buds not resinous (or only slightly so in P. tabulaeformis) 4-. Buds stout, up to 1 inch lonaiiriis nobilis *Li^iistnini vuljjfare Liiulera benzoin Li(|ui(lanibar styraciflua Liriodendron tulipifera Lonicera seinpervirens * tatarica *r.ycium baliniifoliurn Majjnolia grand iflora macropliylla virginiana *Malus sylvestris *Melia azedaraeh ^Moriis alba M 3’rica cerifera Nyssa sylvatica Farthenocissus quinquefolia *Fhiladelphus coronarius *Ficea abies Finns taeda virginiana Flatanus occidentalis *Fopulus alba * nigra *Frunus avium ^ laurocerasus * persica *Funica granatum *Fyrus communis Quercus alba cocci nea marilandica nigra phellos velutina virginiana Rhamnus cathartica Rhododendron arborescens Rliododendron calendulaceum carolinianum nudidorum Rhus aromatica typhina Robinia hispida pseudoacacia Rosa alba Carolina centifolia damascena eglanteria gallica laevigata spinosissima virginiana *Salix babylonica Sambucus canadensis Sassafras albidum Sorbus americana * aucuparia Spiraea tomentosa Stewartia malacodendron Symphoricarpos albus *Syringa vulgaris ^Taxus baccata Thuja occidentalis Tilia americana * vulgaris Tsuga canadensis LTmus americana * procera Vaccinium corymbosum Viburnum prunifolium trilobum Vinca minor Vitis labrusca Wisteria frutescens Donald Wyman [78] A continuation of the Bulletin of Popular Information of the Arnold Arboretum, Harvard University Volume 11 DECEMBER 7, 1951 Number 12 ELMS GROWN IN AMERICA THIRTY-FIVE years ago, Professor Charles S. Sargent, Director of the Arnold Arboretum wrote the following statement concerning the European Elms — unfortunately just as true today as it was then — ‘‘There is probably more con- ! fusion in the identification and proper naming of these trees (the European elms) j in American parks and gardens than of any other group of trees, and it is only I in very recent years that English botanists have been able to reach what appear to be sound conclusions in regard to them. The confusion started with Linnaeus, who believed that all European elms belonged to one species, and it has been in- creased by the appearance of natural hybrids of at least two of the species and by 1 the tendency of seedlings to show much variation from the original types.” Today, with six elm species native in the United States, five species native of Europe (including many varieties), and several more species native of Asia, the I picture becomes even more confused. The elm is, and always has been, a stand - i ard shade tree, for even though it is threatened in certain sections by the Dutch elm disease and phloem necrosis, the gardening public will still plant elms. Ap- proximately fifty elms will be mentioned in this bulletin. About thirty of them S have been listed as available in the nurseries of this country during the past two ! years: all but five of them are growing in the Arnold Arboretum at Boston. I I The Native American Elms ; Of the six native American species, only three are of ornamental value — the American elm {U. americana) and its varieties, the slippery elm {U . fulva) , and the winged elm (U. (data). The winged or wahoo elm is hardy onfv in the south- ern United States, being native from Virginia to Florida and westward to the Mississippi River and Texas, while the other two are native throughout the East and Mid-west. These species are easily distinguishable and little reason exists for j any confusion. A key based on foliage characters is appended to this paper. [79] Rich in references in the early history of the United States, tlie American elm is the most outstandincr and the most deserving of all the elms. It is widely dis- tributed throughout southern Canada, as well as the eastern and the mid-western parts of the L'nited States. In early colonial times, it was under numerous stately specimens that important meetings and many important events took place. Some of these historic elms are still standing today and are well over a hundred feet in height. Many a community in the eastern and mid-western United States has its own local history closely tied to some huge elm which is yet living; and it is the concensus of opinion in hundreds of communities that it would be a dire calamity indeed if the use of the American elm were discontinued in landscape work. There is no ornamental tree just like the American elm. Its wide, vase-shaped form is unique, making it an excellent specimen for lawn and for street planting. Its lofty branches allow much air circulation underneath and, though the tree supplies perfect shade, the widely arching branches do not hinder views from houses. This habit, characteristic of the American elm, is much more evident in mature specimens than in younger trees. Since the habit varies considerably when the trees are grown from seed, it is advisable to propagate vegetatively those in- dividuals of outstanding form. Strangely enough, it is, like the white oak, one of the few of our native trees that does not thrive well in Europe. Several recognized varieties give clear evidence of the diverging habits of the American elm. There is, for instance, the variety columuaris with rather upright branches forming a wide columnar head. The variety ascenclens is more narrow, distinctly columnar. Other columnar or narrow pyramidal forms would include the “Lake City” elm, the “Moline” elm, the “Augustine” elm and the “Prince- ton” elm. Sometimes a variety “wrw/,” or “vase-shaped form,” is found listed in nursery catalogues; this is, in reality, the true U. americana. Then too, there is the variety pendula^ which has all the good qualities of U. americana with the addition of drooping branchlets, making it decidedly graceful. These and other forms should, of course, be asexually propagated in order to perpetuate their characteristic forms. The slippery elm ( U. fulva) is usually found over the same range as the Amer- ican elm but is not such an excellent ornamental and only grows about sixty feet high. Its form is round; its head, broad and somewhat open; and the foliage, not so dense as that of the American elm. From the mucilaginous inner bark of this tree, very popular cough drops were made at one time. The slippery elm is slightly more susceptible to elm leaf beetle injury than the American elm, and need never be used as a substitute for that much better tree. The winged, or wahoo elm (U. a/ata) of the South is a vigorous growing, small tree with a wide-topped head, reaching a height of about thirty feet. The leaves are smaller than those of either of the elms already described, and there are pro- nounced broad and opposite corky ridges along the vigorous young branches. Sometimes the winged elm will grow in protected places as far north as Boston, [80] but it is not dependably hardy north of Philadelphia. Where it can be grown, it makes a vigorous growing, small tree, often with graceful arching branches. It should be given preference to the American elm, however, only where a small sized mature tree is desired. Three other elms, native in the United States, are seen occasionally in culti- vation but these are seldom offered by nurseries because the trees have little to offer as ornamentals when compared with the more beautiful Ulmus americaua . One is the cedar elm iU. crassifoUa) of Texas, Mississippi and Arkansas. It is very common in these states but has been found to be of little value elsewhere in the United States. It is a somewhat round-headed tree, growing about To feet tall and having, like U. alata, opposite corky ridges along the twigs. Closely re- lated is the red elm ( U. serotina) native to Kentucky, Alabama and Georgia but hardy as far north as Boston. It has spreading, somewhat pendulous branches, , forming a broad head ; and it, too, often develops corky wings along vigorous : growing twigs. These two elms and U. parvifolia, the true Chinese elm, are unlike i all other hardy members of the genus in that they develop their flowers and fruits : in the fall and not in the spring. I The last native elm species is the rock elm, U. thornasi (formerly called U. racemosa). Though at present it is rarely grown, the tree might be valuable be- I cause of its unique growth habit. About 90 feet tall at maturity, it usualh’ has a ; central trunk and irregularly developed short, lateral branches, giving an outline which is oblong, rounded at the top, but not necessarily dense. Its slow growth and loosely borne branches are probably the reasons why it has not been much , utilized as an ornamental, but its growth habit makes it easily distinguishable, ! even at a distance, from the rest of the elms. It, too, frequently develops irreg- I i ular corky wings along its younger branches. So much for the native elms. Some are seen everywhere in the East and the Mid-west; and some of the less desirable ones have been left standing where the surrounding land has been utilized for building purposes. As stated before, the last three species mentioned are probably not grown in nurseries nor used in landscape work, but are seen here and there simply because they have remained untouched in areas where man has *\leveloped” Nature's handiwork. The American elm is the best — far superior to the others in every way. Asiatic Elms Of this group, the elm which has caught the public fancy more than any other is the Siberian elm (U. pumila). This plant is a native of northeastern Asia. It is unfortunately misnamed the Chinese elm in many nursery catalogues though this name belongs to U. parvifolia. It was first sent to this countr.v in 1905 b.v Professor J. G. Jack of the Arnold Arboretum and later was introduced in large quantities through the efforts of Frank N. Meyer of the U.S. Department of Agriculture. This vigorous growing tree has found much use in the drier areas [81 ] PLATE XVIII. Elm Species Top row. Ulmus carplnifoHa, serotina, glabra. Middle row. U. amrricana, laehdafa. hollandia I |of the Mid-west, where it does better than most other trees. It withstands clip- ipin^ very well and forms dense hedges and windbreaks when properly clipped. But when we have noted its drought resistance and its fast growth, everything in its favor has been said. It is a weak- wooded tree, does not grow old grace- i fully, and if unpruned, becomes very loose and open. Where other trees are I available for ornamental purposes, they should be grown. This is especially true ■ in the eastern and northeastern United States. Reports are circulating of certain .strains of this tree with good form and habit, which yield similar off-spring when propagated asexually. I have seen several of these trees, which, when young, admittedly make nice specimens ; but it is questionable that they will maintain their good habit as they grow older. For dry soil planting, especially in the dry areas of the West, or for a quick screen which later may be replaced with one more permanent, this tree is admirable; but as a permanent specimen in areas li where other trees are available, it is not to be desired. i An elm frequently confused with U. piimila is the true Chinese elm [U. parvi- native of northern and central China, Korea and Japan. Like U. piimila, ijit has small leaves, one to two inches long. There are several ways in which it [differs from the taller growing Siberian elm, however. The true Chinese elm is ta small tree, usually under fifty feet in height. It has thin scaling bark and a round-topped crown, keeps its foliage green until late in fall and is half ever- ligreen in the south. It bears its flowers in the fall while U. piimila has them in :the spring. Usually, like the other elms, its autumn foliage is bright yellow; but two of the trees in the Arboretum have a bright red autumn coloration. It has ;been noted in the Japanese beetle area around Philadelphia, that where these itwo species were growing side by side, the beetles would practically defoliate U. \pinnila and scarcely touch U. parvifolia — an interesting observation well worth further investigation. 1 The Japanese elm ( U. Japonica) has long been a tree of importance to the Ainu, the aboriginal people of Japan. Many of these people believed that this was the first tree created, sent directly from heaven in full growth. This tree plays an important part in their economy. Fire is made by rubbing its dry roots together. rjWhen the inner bark of the tree is mashed and mixed with water, it is woven I into a cloth from which wearing apparel is made. The outer bark is used in the f roofing of houses and as covering for the outside (and the inside) walls. The 6 Japanese elm is a handsome tree with good dark green foliage. It is as important ■j ornamentally as the Scotch elm because of its similarity in general appearance, iln the collection at the Arnold Arboretum, it is susceptible only to a very slight 'infestation of the elm leaf miner and the elm leaf beetle. 1* The fourth and last A.siatic elm, the Manchurian elm (U. laciniata) is of little ij importance ornamentally simply because it does not have a good habit of growth. 1 All the trees in the collection at the Arboretum have a fan-shaped habit of ; branching, with a correspondingly rounded head, but the leaves are borne only [83] at the tips of the long branches, which liave very few side shoots. This plant has been offered in a few American nurseries but might well be replaced by some of the better elms. European Elms 'riiere are three elm species which, strictly speaking, are native of FLurope only. They are the Fbiglish elm, U. procera (formerly called U. campestris) , the Itussian elm (V. laevis), and the Plot elm {U. ploti). Characteristic of the Fmro- pean elms as a group is the fact that they all assume their autumn color later in the fall than do the native American elms. Of the three, the English elm is by far the most important in ^America. Many of these trees were planted in Massachusetts in the eighteenth century and since that time have been continually used as street trees and specimens throughout the F^ast. F.. H. Wilson strongly recommended this tree for city planting for he claimed it withstood the smoke and obnoxious gases of the city better than any of the other elms, the American included. It does not have the queenly arching habit of the American elm, but it does have a grace and beauty all its own, with its numerous ascending and spreading branches. It has also been noted that in good seasons the leaves remain green several weeks longer than do those of the American elm. Unfortunately it is most susceptible to attacks of the elm leaf miner and of the elm leaf beetle. Several varieties of the F^nglish elm are known, but none of them are grown in quantity by American nurseries. The variety vauhouttei has leaves tinged with yellow, and aurea actually has yellow leaves. The variety purpurascens has pur- plish leaves, and another variety, marginaia, has leaves with a creamy-white mar- gin. One form, australis, has leaves that are much thicker and firmer than those of the species. Perhaps the best ornamental variety is myrtifolia, which has the smallest leaves of any of the elms — scarcely one inch long. The European white elm or Russian elm, U. laevis (formerly U. pediawu/ata), is common in some parts of the Scandinavian Peninsula and Russia. It is similar in size to our own native American elm and is as hardy. Fiowever, it differs because it has a much thicker coating of tomentum on the undersurface of the leaves, and longer, more sharply pointed buds. In England, it grows better than the Amer- ican elm. It is apparently rare in American collections, but makes an excellent specimen tree, with a single upright main trunk. Another European species is the East-Anglian or Plot elm, U. ploti. The name lock elm was given to it in England because of the difficulty of working its tough wood. This tall growing tree, which reaches a height of 80-90 feet is closely allied to the Scotch elm and is rarely found in American collections. The next elm species to be mentioned is a hybrid, U. hollaudica, apparently a hybrid of U. glabra and U. carpiuifolia . There are a number of varieties but the one which well might represent this group is known as variety major, commonly called the Dutch elm. It is a tree of over 100 feet with a short trunk, wide- [ 8-1] Ulmus parvifoUa sempernirens growinfj^ in the Huntington Botanic Garden, Pasadena, California. Young plants propagated from this tree have survived three winters in the Arnold Arboretum, but have dropped their leaves only slightly later than the species. However, it is practically evergreen in southern California. spreadinji' branches and lustrous dark jrreen leaves. Other varieties have been planted to some extent in F.urope as street trees and a few have met with favor in America. 'I'lie Bel^iian elm, r. hoUaudicd he/gica, is a tall, rough-barked tree with a straight trunk. Younger trees are dense and pyramidal in habit while older ones may he more or less cylindric. 'frees of this variety in the Arnold Arbore- tum are apparently somewhat more hardy than tyi)ical U. hoUandica major. The Klemmer elm (var. ‘^Klemmer”) has smooth hark, tall ascending branches and a narrow pyramidal habit of growth. It originated in Belgium where it is planted a great deal, 'fhe Huntingdon elm (rege/r/) originating about 1750 has been used in America and is valued for its height, its forked trunk and its rough bark. A narrow pyramidal variety with smooth bark is superba and still another variety, pendida, originating in England about 1830, has ascending branches but pendu- lous branchlets. Species Native of Both Europe and Asia 'fhe last two species are native of Europe and Western Asia and are used a great deal in the United States because of their good ornamental characters and their several horticultural forms. 'fhe first is the smoothleaf elm U. carpimfolia (formerly called U. foViacea or U. niteus). Being used to a great extent in this country, it is constantly confused with the English elm, U. procera {U. campeslris), from which it may be distin- guished by its less deeply furrowed bark, mostly glabrous branchlets, longer and often obovate leaves which are lustrous and usually smooth on the upper surface with petioles from 4 to inch long. Unfortunately, the seeds of this tree have been sold for years by European seedsmen as U. campestris; consequently, the resulting confusion in this country has been inevitable. The smoothleaf elm, which may reach a height of 90 feet and is quite variable in growth habit, has many horticultural forms, some of which are available from nurseries in this country. This tree usually is pyramidal in outline, having a single trunk and somewhat ascending branches, although sometimes the branches may be pendulous and the head more or less rounded. In the south of England, it is often referred to as the Herfordshire elm and grows with a broad head and rather pendulous branches, surpassed in beauty only by the American elm as it grows in New England. The pendulous branched form ipendida) has been offered by American nurseries. An unusual variety is xcebbiana, of little horticultural value because, even though the tree is narrow and pyramidal with ascending branches, the leaves are folded longitudinally, giving the appearance of wilting. Another form, variegata, has its leaves blotched with two shades of green and with white; and though not particularly desirable, it is of interest to those who like trees with variegated leaves. Eight other varieties of the smoothleaf elm have horticultural significance, six of them being offered in American nurseries. Both the Cornish elm {coruubieusis) [8(i] : and the Wheatley elm {saruiensis), incorrectly called thouj^h also known as the Guernsey or Jersey elm, are narrow, pyramidal trees with dense, erect branches. The Wheatley elm, almost columnar in habit, has a slightly broader head and wider leaves than the Cornish elm, with branches more stiffly erect. The variet.v dcimpieri is a fastigiate tree with a very narrow, pyramidal crown and deeply double-toothed leaves ; ivredi is similar but its leaves are yellowish. Another ’ variety, named suherosa, is little more than a dense shrub, irregularly cylindric ( in outline, the young sucker branches of which frequently develop opposite corky wings. Somewhat similar to siiberosa is the variety propendens , the branches of which are pendulous and its leaves are very small, only being about one inch long. An outstanding elm was sent to Germany from Persia in 1878 and has since been named the variety umbraculifera . This is a dense growing, small tree with a glo- bose or sometimes flat top and erect branches. Closely associated to it is the variety koopmanni, which is definitely more globose in outline but just as dense. Trees of these two varieties in the collection at the Arnold Arboretum are well 1 clothed with branches from top to bottom. These unusual forms are not to be desired in preference to other more orna- mental trees and shrubs in the landscape, but they do have a definite use. Some- times there is a place in a large plant area for a small tree with a definite outline — something which does not require constant pruning to keep it in shape. These ‘ varieties of the smoothleaf elm supply just such an accent point. Indiscriminate use of these trees, however, should be guarded against. The other elm species which is native of Europe as well as certain parts of western Asia, is the Scotch or Wych elm, U. glabra, sometimes formerl.v called V. montana or U. scabra. This tree, with wide-spreading branches and often flat- topped head, is used considerably in America as an ornamental. The dark green leaves, sometimes with two or three points near the apex, are broader beyond the middle, very rough above and downy underneath. The petioles are about ^ inch long. Unlike many of the other elms, this one does not produce suckers; and on account of this good trait, it has been used much as an understock in ; grafting. Unfortunately, it is one of the first elms sought by the elm leaf miner and in locations where there are several varieties, this pest does more injury to I this tree than to most of the others. This elm can always be distinguished from other European elms by the fact j that the seed is in the middle of the fruit, the petioles are very short, the upper i surface of the leaves is rough and there is an absence of corky ridges on the two- ' year branches. The specific name glabra comes from the fact that the branches ; are very smooth, not rough like most of the other elms. A number of varieties of this are grown. The most popular is the Camperdown elm {camperdoui'n'i) which, when grafted on an upright stem, has a wealth of pen- dulous branches forming a globose head. Many such trees can be seen even in ' this country, forming natural arbors, under which chairs and tables are placed. [H7] The Moline Elm as it is f^rowing in Moline, Illinois. (Courtesy of the Schultz Studio and the Park Department, Moline, Illinois.) Another form {pemlula) has rather horizontal branches with pendulous branchlets and grows into a low flat-topped tree. There is a fastigiate variety, called the Exeter elm {exoniensis, formerly U. monfaua fastigiata), with rather small, often wrinkled leaves, but with branches rigidly upright. One variety {purpurea) has leaves which are purple in color when they are young; another variety iatropur- purea) retains the color in the leaves for a longer period. A compact shrub with smaller leaves is the variety moustrosa. A lower growing bush is uana^ which sel- dom grows over 6 feet tall. Sometimes this bush elm is grafted 6 feet up on the trunk of U. glabra, resulting in a dense, compact, round-headed tree. xA curious, slow-growing form with leaves that are narrow and crinkled is called crispa — used sometimes because of its queer foliage. This is not the time nor the place to enter into a discussion of the two serious pests that are now doing tremendous damage to the elms. Much has been writ- ten recently about the inroads of these two serious diseases east of the Mississippi River, and the Dutch Elm Disease is now as far west as Denver, Colorado. Much research work is being done by the U.S. Department of xAgriculture on control methods for these pests, and anything that might be said on that score here, might well be antedated in a year or so. Suffice it to say, that most elms are susceptible to both diseases, some species more than others. \’^igorous, well-grown trees, well pruned, sprayed and ferti- lized, seem to have a better chance of escaping these diseases in infested areas than do sickly trees that are greatly in need of attention. It would seem that no one should plant elms without a thorough knowledge of the situation. Especially is this true of those responsible for the expenditure of large amounts of public funds in planting trees along the streets and highways, for they have a respon- sibility to the future population as well as the present. If a long line of elms were set out now, with trees dying out intermittently during the next fifteen or twenty years, this would indeed be poor planning. There are enough other trees from which to choose for street or highway planting, so that elms might be overlooked in such planting plans for the time being at least. The policy should be, especially in disease areas or those adjacent to them, to use other trees where at all possible. Latest control methods should be thoroughly known and understood when planting large numbers of elms. Elms should now be planted only in situations where it is a foregone conclusion that they will re- ceive the best annual care. The Key The following key is offered as an aid to the identification of elm species on the basis of foliage characters. More exact keys have been made, in which the flow- ers and fruits are used, but many an amateur is confronted with the perplexing problem of identification when flowers and fruits are not available ; hence this key. Every one of the elm species varies greatly, and to make a key using only [ 8!) 1 one or two characters is not very satisfactory. 'J'herefore, tliis key is not infalli- ble, but it may serve its purpose to many who are perplexed concerning the identification of these elms. i 'I'o the individual not familiar witli the use of keys, this may at first seem con- fusing, but careful study may prove its simplicity. For instance, all elm species fall into one of four groups (marked by the figure l), because of corky ridges on the brandies, or leaves with several points at the apex, or leaves simply serrate, or leaves doubly serrate. To place a plant in one of these four groups, these four ; characteristics should be used in this sequence. Once done, the remaining points ; should be taken up in the particular group, in the sequence suggested in the key. \ Identification will be aided materially if the habitat of a tree is known. For in- stance, in the first group (corky ridges on the branches) Uhnus crassifolia would not be found in northern Minnesota, nor would it be likely that U. procera and U. japonica would be found growing wild in the woods. ; Be certain that the tree is examined carefully for all possible marks of identi- fication, and that many leaves are examined since one alone would not tell the full story. It should be noted that this key does not take into consideration the varieties | of these species, many of which can be identified by their form alone. Also, and this is very important, it should be noted that the following species are not com- , mon in America except in botanical collections : U. japonica, laevis, ploti, and i that other species, like U. thomasi and serotina, are used very little in landscape i work. A knowledge of these facts should make this key much more usable. | The elms are so variable that it is likely they will continue to be difficult to | identify for many years to come. These notes and suggestions are offered merely i as aids to those interested in this group of trees. | ABBREVIATED FOLIAGE KEY TO COMMON ELM SPECIES 1 . Corky ridges or wings on younger branches 2. Leaves simply serrate 2. Leaves doubly serrate Uhnus crassifolia 3. Young twigs glabrous or nearly so 4. Wings usually two and opposite 4. Wings several, not necessarilj' opposite, flowers in spring, U. alata not native U. carpinifolia suherosa 4. Wings several, not necessarily opposite, flowers in fall, native 3. Young twigs pubescent U. serotina [ 90 ] I PLATE XXI Ulmus americana columuaris. Several clones of this upright variety have been named and are available from commercial sources. This picture was taken by R, E. Horsey, formerly of the Rochester, X.Y. Park Department, at the time the tree was dO feet tall with a branch spread of only 18 feet. U. thomasi 4. Free irregularly columnar 4. Tree not irregularly columnar, oval or rounded in outline 5. Leaves "2-3" long, wings occasionally U. procera 5. Leaves 3-4.75" long, wings occasionally U. japonica Leaves three pointed at tip or occasionally so, branches not corky 2. Mature branches reddish brown, hairy while young; leaves occasionally with one or two extra points at apex 2. Mature branches pale yellowish or grayish brown, glabrous or nearly so when young; most of the leaves three-pointed at apex 1. Leaves simply or nearly simply serrate, 0.75-2.75" long 2. Leaves often nearly equal at base, many leaves showing in- dications of double serration, young branches pubescent or glabrous, stipules broad, flowers in spring 2. Leaves usually unequally rounded at base, young branches pubescent, stipules linear, flowers in fall 1 . Leaves doubly serrate 2. Young branches glabrous 3. Leaves 2.75-6" long 4. Leaves usually twice as long as wide, no conspicuous axillary tufts of hair 4. Leaves less than times as long as wide, usually with conspicuous tufts of hair in axils of veins on under sur- face of leaves, considerably variable 3. Leaves 1 .25-3.25" long 4. Petioles 0.25-0.5", leaves 2-3", smooth above 4. Petioles less than 0.25", leaves 1.25-2.25", slightly scabrous above 2. Young branches pubescent 3. Leaves often glabrous beneath 3. Leaves pubescent beneath 4. Leaves 2-3" long 4. Leaves longer 5. Leaves often widest at middle, 4-8" long [92] U. glabra U. laciniata U. pumila U. parvifoJia U. americana U. hoUamlica U. carpiinfoUa U. ploti U. americana U. procera U. fulva 6. Branchlets grey to light brown, buds covered with rusty brown hairs 6. Branchlets dark brown, buds without rusty brown hairs, leaves sometimes showing a tendency to be three pointed at tip 5. Leaves usually widest above middle, 2.5-4.75'' long 6. Leaves scabrous and pubescent above, corky wings on branches occasionally I 6. Leaves usually glabrous above, very unequal at base Donald U. glabra 7. japonica U. laevis Wyman [93] INDEX TO VOLUME XI Illustrations are in bold face type ^ Acer platanoides, 71 Air Layering experiments, materials used, Plate XIII, 53 on Malus “Dorothea,” Plate XIV, 60 , plants that rooted, 54-57 , plants that failed to root, 57— 61 , results, 61 , 62 with Polythene Film, 49-62 “Alathon,” 50 American Elm, 41 Berberis julianae, 3 — koreana, 3 “Bon-sai,” the art of training dwarf trees, 30 Buxus microphylla koreana, 4 Chamaecyparis obtusa, Plate IX, 31 Chionanthus virginicus, 4 Clethra alnifolia rosea, 4 Cornus alba sibirica, 6 Cotoneaster dammeri, 6 — divaricata, 6 Crataegus monogyna inermis, Plate XIII, 46 “Crimson King” Maple, 71 Cytisus praecox, 6 ; Plate I, 5 Davidia involucrata, 72 Dawn Redwood,” 28 “Dura-Clear,” 50, 51 Dutch Elm Disease, 41, 89 Dwarf Trees, Pruning, Repotting and Watering, 35 , Training, 32 , Winter Protection, 35 , Native of both Europe and Asia, Elms, Asiatic, 81-84 — , European, 84-86 — , Grown in America, 79-93 — , Key to, 89-93 — , Native American, 79-81 — , Native of both Europe and Asia, 86-89 Elm Species, Plate XVIII, 82 Enkianthus campanulatus, 7 Euonymus alata compacta, 7 Evergreens in Governor’s Garden, Williamsburg, Va., Plate XVII, 78 Five Interesting Trees, 71-74 Fothergilla species, 7 Gleditsia triacanthos, 71 Ground covers already established, 22-44 Ground cover demonstration plot, Plate VII, 23 Grove, Colonel William R., 49 Hamamelis mollis, 7, Plate \', 17 — vernalis, 7 “Howard-Seal, ” 50 Hypericum species, 8 Ilex crenata convexa, 8 ; Plate II, 9 Japanese Dwarf Trees, 29-35 Juniperus chinensis sargenti, 8 Key to the Pines, Simple, 63-70 Larz Anderson Collection of Japanese Dwarf Trees, The, 29-35 Leucothoe catesbaei, 8 Lonicera amoena arnoldiana, 10 — bella, 10 — korolkowi floribunda, 10 Magnolia stellata, 10 Mahonia aquifolium, 10 Malus sargenti, 1 1 Mains torinfjoides macrocarpa, 72 Metasequoia Broujjht Up To Date, 0 5-28 — glyptostroboides, 25,72; Plate VII 1, 27; Plate XVI, 78 Moline Elm, The, Plate XX, 88 “Moraine Locust,*’ 71 New Ground Cover Display Plots, The, 21-24- “Pearlon,” 50 Philadelphus lemoinei “Avalanche,” 1 1 — splendens, 1 1 — virginalis, Plate XI, 39 Pieris floribunda, 1 1 — japonica, 11 Pinus albicaulis, 64- — aristata, 64- — attenuata, 66 — banksiana, 68 — bungeana, 66; Plate XV, 67 — canariensis, 66 — caribaea, 68 — cembra, 64- — cembroides, 68 parry ana, 66 — coulteri, 66 — densiflora, 68 oculus-draconis, 68 imibraculifera, 68 — echinata, 68 — flexilis, 64- — griffithi, 64- — jeffreyi, 66 ; Plate X, 33 — koraiensis, 64 — lambertiana, 64 — monticola, 64 — mugo, 68 com pacta, 68 pumilio, 68 — nigra austriaca, 68 — palustris, 66 — parviflora, 64 glauca, 64 — pence, 64 — pinaster, 68 — ponderosa, 66 scopulorum, 68 — pumila, 64 — pungens, 68 — radiata, 66, — resinosa, 68 — rigida, 66 — sabiniana, 66 — strobus, 64 fastigiata, 64 nana, 64 — sylvestris, 68 — tabulaeformis, 68 — taeda, 66 — torreyana, 64 — thunbergi, 68 — virginiana, 68 Plants used in Williamsburg, Va., Prior to 1750, 76-78 Plastic films, properties of, 50, 5 1 “Pliofilm,” 49 “Polyethylene,” 50 “Polythene,” 50 — , Properties of, 50, 51 Potentilla fruticosa, 12 Rhododendron arborescens, 12 — calendulaceum, 12 — gandavense, 12 — mucronulatum, 14 — schlippenbachi, 14 — smirnowi, 14 — vaseyi, 14 Rosa multiflora, 14 Seed Germination, effect of light on, 40 Sentry Gingko along Roosevelt Blvd. Plate XII, 43 Shrubs for American Gardens, 1-20 [96] Shrubs for at Least Two Seasons of Beauty, Some, 37-40 Street planting, 42 Street trees, 41-48 , size of at planting time, 44 ,' suburban planting, 44 Syringa persica, 16 Syringa prestoniae “Isabella,” Plate VI, 19 “Hecla,” Plate VI, 19 \ ars. , 1 6 Taxus cuspidata nana, 16 “Tralon,” 50 Trees, Five Interesting, 71-74 — , Narrow for Narrow Streets, 48 — , Small for City Streets, 47 — , Small Street Trees Needed, 41-48 Tsuga canadensis pendula, 18 — diversifolia, 18; Plate IV, 15 LTmus alata, 79, 81, 90 — americana, 79, 80, 81, 92 ascendens, 80 “Augustine,” 80 columnaris, 80 ; Plate XXI, 90 “Lake City,” 80 “Moline,” 80 pendula, 80 “Princeton,” 80 — campestris, 84, 86 — carpinifolia, 84, 86, 92 cornubiensis, 86 — - — dampieri, 87 — - — koopmanni, 87 pendula, 86 propendens, 87 sarniensis, 87 suberosa, 87, 90 umbraculifera, 87 variegata, 86 webbiana, 86 wredi, 87 — crassifolia, 81, 90 — foliacea, 86 wheatleyi, 87 — fulva, 79, 80, 93 — glabra, 84, 87, 89, 92 atropurpurea, 89 camperdowni, 87 crispa, 89 exoniensis, 89 monstrosa, 89 nana, 89 pendula, 89 purpurea, 89 — hollandica, 84, 92 belgica, 86 “Klemmer,” 86 major, 85, 86 pendula, 86 superba, 86 vegeta, 86 — japonica, 83, 90, 92, 93 — laciniata, 83, 92 — laevis, 84, 90, 93 — montana, 87 fastigiata, 89 — nitens, 86 — parvifolia, 81, 83, 92 sempervirens, Plate XIX, 85 — pedunculata, 84 — ploti, 84, 90, 92 — procera, 84, 86, 90, 93 aurea, 84 australis, 84 marginata, 84 myrtifolia, 84 purpurascens, 84 vanhouttei, 84 viminalis, 84 — pumila, 81, 83, 92 — racemosa, 8 1 — scabra, 87 — serotina, 8 1 , 90 — thomasi, 81, 90, 92 [97] Viburnum dilatatuiTi, 18 Viburnum sieboldi, 18; Plate III, IS — tomentosum, 20 ‘^Visqueen,” 50 “V^itafilm,” 49 Williamsburg, Va., Plants used prior to 1750, 75 Woody Plants used in Colonial Williamsburg, 75-78 I [ 98 ]