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VOLUME JV 1936 PUBLISHED BY THE ARNOLD ARBORETUM JAMAICA PLAIN, MASSACHUSETTS ILLUSTRATIONS The Old Lancaster Elm, 17 Hamamelis mollis, H. japonica, H. japonica Zuccariniana, and H. vernalis, 25 Magnolia stellata, photographed by Alfred Rehder, plate facing page 28 Early-flowering Rhododendron dauricum var. mucronulatum, plate facing page 29 Japanese Spring Cherry (Prunus subhirtella), 38 Malus hupehensis, plate facing page 86 Syringa vulgaris **Congo”, 41 The Chinese lilac (Syringa chinensis), 45 A good hybrid. Rhododendron “Album elegans,” 58 Double-dowered Philadelphus virginalis “Albatre,” 57 The handsome Philadelphus splendens, 61 As a bush. Tripterygium Regelii, 65 Fleece Vine (Polygonum Auberti), plate facing page 68 Campsis radicans, C.Tagliabuana, C. grandiHora, plate facing page 69 Cotoneaster racemidora soongorica, 75 Most beautiful crabapple in fruit, Malus toringoides, 80 Digitized by the Internet Archive in 2017 with funding from BHL-SIL-FEDLINK https://archive.org/details/bulletinofpopula04arno_2 ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV MARCH 21, 1936 Number 1 TREE TROUBLES Not all trees keep in good healthy condition, and it is the purpose of this bulletin to mention some of the causes why we have ^^sick’* trees, together with some recommendations for their ^Ture.” The recommendations made are not primarily the results of any in- vestigations at the Arboretum, but rather from various experiment stations throughout the eastern United States. Though suggestions are given on fertilizing it must be kept in mind that with wide varia- tions in soils, in trees and in their root systems, any specific recom- mendation given to cover all conditions should be taken only at its face value. Efforts should be made by those interested to investigate thoroughly local conditions and try to suit any general recommenda- tions to their particular needs. Illuminating Gas in the Soil. Gas, leaking from mains, gets in the soil and may cause the death of trees. Even a very minute leak may, over a period of a few years, be sufficient to cause a nearby tree to die. An ingenious method has been devised at the Boyce Thompson Institute* to determine the presence of illuminating gas in the soil. Of course, if gas is known to be present by its odor, then there is no need for the test, but often tlie damage is done by an amount of gas in the soil, so small that it cannot be detected by its odor. The test includes placing a young tomato plant in a hole in the ground, leav- ing it covered for twenty-four hours and observing its reaction when uncovered. If gas is present, the leaves will show a very definite type of wilting. *Toxic action in soil of illuminating gas containing hydrocyanic acid. By A. E. Hitchcock, William Cocker and R. W./immerrnan. Boyce Thompson Inst, for Plant Research Contrib. (L l-BO. IfIB t. [1] If illuininatino: jjas is present in the soil, no trees should be planted until the leak has been definitely and positively stopped. When this is done, the soil should either be removed entirely or be washed tho- roughly so that all the soluble poisons are taken out of the soil. If the drainage is poor, tile drains should be put in since this washing process should be a complete one. When this has been done satisfac- torily, new trees may be planted. Raising the Grade. liaising or lowering the grade around a tree may cause serious damage. The feeding roots of most trees are usu- ally within the upper 18 to 24- inches of soil. At this depth there is a certain amount of oxygen in the soil air spaces, while at lower depths there is usually less oxygen, more carbon dioxide and possibly less water. Since roots need a certain amount of oxygen, and large amounts of carbon dioxide are injurious, when soil is piled on top of the existing level under a tree, conditions for root injury are aug- mented. A fill of a few inches of soil on top of tree roots is not harmful, but a fill of 18 inches or more may prove decidedly harmful, depend- ing on the type of tree, type of soil, amount of rainfall, drainage and the like. If a considerable fill is to be made the procedure is as follows: The surface of the old grade is loosened ; several lines (at least four) of 4-inch agricultural tile radiating out from the trunk of the tree like the spokes of a wheel, are laid as far as the spread of the branches; a layer of coarse stone or large screened gravel is used to cover the tile and to raise the grade to within 15 inches of the final lawn sur- face. On top of this is placed a 2-inch layer of smaller stone or peb- bles, and on top of this a layer of straw, or better a layer of manure, or some similar material, in order to keep the dirt from sifting down through the rock layer. The top soil is then added to the finished grade. This treatment should be made over the entire area of ground covered by the tree branches. At the same time a “well” is built around the trunk of the tree to the top of the proposed soil level. This “well” is from 3 to 4- feet in diameter, or larger, depending on the size of the tree, and is made to allow air and water to enter the tile and the layer of crushed rock after the filling has been done. In this way, air and moisture can reach the tree roots no matter how deep the fill is. This treatment also makes it possible to water the tree very effectively during dry weather. Gas in the Air. City conditions are hard on plant life largely be- cause of the injurious gases and soot in the air. The soot and dust [2] fall on the leaves and clog the stomates, thus preventing the normal intake of carbon dioxide. Also the gases contained in the air of the city, especially sulphur dioxide, are injurious to plant life. Some trees, such as ^^lanthus, Catalpa, poplars and willows are more resistant than others to these variable conditions. The conifers, as a rule, are the most susceptible to this injury. If these conditions are present, one should observe the trees doing best in the vicinity and plant them, rather than trying a long series of untried and often disap- pointing types. Painting Wounds. Experiments have shown that wounds heal most quickly when the pruning is done between February 1 and May 1. While many small wounds may heal over quickly enough to pre- vent infection, still it is best to paint all wounds 2 inches or more in diameter with some good durable wound dressing. At the present time the best paint for wounds, listed in order of their merit, are as- phaltum, orange shellac, white and red lead paint and bordeaux paste. One of these should be applied immediately, as soon as the cut has been smoothed olf, except on trees like the maples and birches, which ^^bleed” profusely in the spring. Such trees should be pruned only in the late spring or summer when the wood remains dry enough to paint. Asphaltum is probably the best type of paint to use on wounds, providing a thin covering can be obtained. Several commercial as- phaltum paints are on the market, some of which are thin enough so they can be used in cold weather without heating. This is the type to use. Thick asphaltum paints are not recommended, for they easily ‘^blister” and are very hard to use properly in cold weather. The large ^^blisters*’ caused by moisture collecting under the surface even- tually break the covering and provide a source of infection by the large opening they leave in the covering itself. Orange shellac is about the least harmful to the cambium tissue of any of the paint wounds. It can be appled in cold weather but is often objectionable on account of its brilliant orange color. It also tends to crack, particularly on large wounds and may have to be retouched once or twice a year. White or red lead paints are objectionable in color and are slightly injurious to the cambium ; but tliey are effective and are usually avail- able. Wounds should be re])ainted, when necessary, once a year. Bordeaux Paste is made by mixing dry commercial bordeaux mix- ture with enough linseed oil to form a thick paste. As a wound paint it has the desirable property of being sliglitly porous to moisture and [3] air, and at tlie same time is a furifjicide. Blistering does not occur underneath this dressing. Its outstanding drawback is its color, which passes through changes of blue to green after it has been applied. Apparently little is accomplished by painting over it, since the multi- colored copper salts eventually appear on the surface. Tree Repair. Tree repair is a study in itself. It is usually unwise, and often impossible, for the inexperienced person to attempt to fill cavities. In fact, some question the value of filling tree cavities at all, believing that trees are better off if the cavities are cleaned out, painted properlv and left alone. This subject is too broad for discus- sion here. At least a cavity should have all the diseased wood cut out, the remainder smoothed over and then painted, preferably with a good fungicidal paint like bordeaux paste. A coat of asphaltum may be added over the bordeaux for permanence. One other thing the amateur can do is to brace some of the bad crotches in the older trees. This is never accomplished by completely encircling the limb with a wire, but by putting an eye bolt through each limb and connecting these two bolts with an iron rod or heavy cable. Each eye bolt should have the washer and nut completely countersunk on the outside so that the bark may heal over quickly. Fertilizers. Lack of sufficient nutrients in the soil is only one of many causes for “sick” trees. The addition of fertilizer to the soil about a tree is not a cure-all, and should only be attempted when one is certain that malnutrition is the cause of the poor condition. Ex- periments on a wide range of soils, over a long period of time, have shown that in the United States at least it is nitrogen which is most frequently deficient in the soil, and possibly phosphorous. Well rotted manure is always good as a fertilizer, not only because it has a high nitrogen content, but also because it contains much organic matter which aids the soil in retaining moisture. However, many trees can be aided materially by simply broadcasting on the surface of the soil under the tree ammonium sulphate or sodium nitrate (both of which contain a high proportion of nitrogen with no phosphorous or potash) ; or ammophos, a trade name for a material very similar to ammonium sulphate except that it contains phosphorous in addition to nitrogen. Shade trees may be fertilized either in the fall or in the spring. Spring fertilizing is often preferred because then, if a readily avail- able fertilizer is used, increased growth will result the same year. If the tree is not in a valued lawn, such a fertilizer may be broadcast underneath the branches and washed in with water, but it must be remembered that large amounts of commercial fertilizer spread indis- [4] criminately on the o-rass may seriously injure it. Tests at Cornell Uni- versity have shown that amounts of ammonium sulphate as hi^h as 30 pounds per 1000 square feet can be applied to a grass plot without in- jury to the grass, providing application is made before the grass be- gins to grow in the spring. On the other hand, there are many fertilizers on the market for shade trees with nutrients which are not so readily available to the plant as ammonium sulphate or ammophos. If such a fertilizer is ap- plied, or if there is any danger from injuring a highly prized lawn with too much fertilizer, then the crow-bar method of applying the fertilizer should be used, as follows. Method of Applying Fertilizer. A circle is drawn on the ground under the outside limits of the branches of the tree, and another circle is drawn two-thirds of the way towards the trunk. The area between these two circles is the area to be fertilized. Holes about 15 inches deep are then dug with a crow bar, soil augur or automatic drill, and the fertilizer so divided so that a small amount is placed in each hole, and the soil replaced. The amount of fertilizer in each hole depends largely on the kind of fertilizer, if it has a high amount of readily available material in it, as does ammonium sulphate, then only a few ounces should be put in a hole. The holes themselves should not be more than 3 feet apart, preferably less, for the more evenly they are distributed, the better the results. In fact, some commercial concerns are now actually blowing the fertilizer into the soil in order to get better distribution. However, trees should not be fertilized, in general, until at least one year after transplanting, since the first year the tree is much more dependent upon its new water relations, that is, the amount of v/ater which can be taken in by the roots as compared with the amount given off by the tops. The first year then, water the tree well, mulch it if necessary to give it additional moisture around the roots, but do not give it the highly concentrated commercial fertilizers. Some well rotted manure is satisfactory for this aids materially in conserving the moisture in the soil, but it must be well rotted. Amount of Fertilizer to Use. Most fertilizer recommendations are based on the size of the tree trunk, implying that the size of the trunk is an accurate criterion to the general size of the tree. Fertilizers vary considerably with the amount of readily available material in them, and that is why some are to be used at the rate of only 1 j)ound per inch in diameter of tree trunk, and some at 3 pounds. Ammonium sulphate and other similar materials can be used at the rate of ^ to 1 pound per diameter inch of tree trunk on mature trees and even more on very larj^e trees. Such materials should he used with caution on evergreens and deciduous trees under 4 inches in diameter. A 10-20-10 fertilizer (that is, containing 10 parts nitrogen, 20 parts phosphorous and 10 parts potash) can be recommended at the same rate, the larger amounts for the larger trees. There are many such mixtures on the market, varying considerably in the amount of readily available nitrogen. The larger the amount of readily available plant food in the fertilizer, the smaller the ai)plication should be. Well rotted manure, forked in under the trees is always good, and in a jdace like the Arboretum is one of the best and cheapest fertil- izers which can be used. For Deciduous Shrubs and Evergreens. The best general recom- mendation for deciduous shrubs and evergreens is to regularly mulch them in the winter with well rotted manure, rotted leaves or other quickly decomposing organic matter. Particularly is this true of ever- greens, at least until more is known about their reactions to commer- cial fertilizers. No commercial fertilizer should ever be placed in the hole at transplanting time. At maturity, most shrubs maintain a fairly definite height, and it is foolish to fertilize such plants in the hope of making them grow taller. Also, when excessive amounts of nitro- genous fertilizers are given to certain shrubs valued for their flowers and fruits, they make a greater vegetative growth at the expense of flowers and fruits. With some shrubs (Wisteria and flowering dog- wood) it has been found that a phosphatic fertilizer such a superphos- phate, mixed with the soil in a trench dug around the plant, may aid in producing more flowers the following seasons. If commercial fertilizers are to be used on the shrub border, then a 5-10-5 might be applied at the rate of ll to 2 pounds per 100 square feet. A 10-20-10 might be used at half this rate. In growing nursery stock, stronger applications than these have been used. In fertilizing woody plants it should always be kept in mind that there is a time during the summer when no fertilizers whatever should be applied. For, if application were made at this time, increased growth might result in the early fall which would not have sufficient time to mature before the killing frosts came. Consequently, fall fer- tilizing might best be done at any time after the first of September. Donald Wyman [6] BOOKS There are several books and many bulletins on the care of trees. A few of the outstanding ones might be : Felt, E. P. and Rankin, W.H. Insects and diseases of ornamental trees and shrubs. New York. 1932. Macmillan Compan.y. Herrick, G. W. Insect enemies of shade-trees. Ithaca. 1935. Com- stock Publishing Company, Inc. Le Sueur, x\.D.C. The care & repair of ornamental trees in gar- den park and street. London. 1934<. Country Life, Limited. Marshall, R. P. The relation of season of wounding and shellacking to callus formation in tree wounds. Washington. 1931. U. S. Department of Agriculture. Technical bulletin, 246. [7] ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV MARCH ‘25, 1936 Number 2 INSECT CONTROL AT THE ARNOLD ARBORETUM IT is the purpose of this article to give a practical summary of the problems in relation to insects effecting trees and shrubs, report- ing methods of control that are used at the Arnold Arboretum. Though other materials and methods might give just as satisfactory results, only those will be reported which have been used over a period of years in the Arboretum and have proved satisfactory. Considerable thought should be given as to the right kind of equip- ment used in the spraying of trees in parks or private estates. Here at the Arboretum we find that a 300 gallon sprayer, mounted on skids, with a 32 horse power motor that is capable of throwing a stream 80 feet with 350 pounds pressure, is very satisfactory. This sprayer, weighing 1620 pounds, can be loaded on a H ton truck in a very few minutes from a platform. When not in use the truck is available for other work. Our first problems are the scale insects. There are several kinds ot these which do damage to shrubs, fruit and shade trees; namely, oyster-shell scale, San Jose scale, scurfy scale, evonymus scale, pine leaf scale that also affects spruces, and juniper scale. All of these scale insects obtain their food by sucking out the plant juices from the twigs and limbs, thus materially weakening the plant. Oyster siiell, San Jose and scurfy scale may be found on apples, lilacs, plums, peaches, poplars and willows. They can be controlled by spraying with miscible oil, 1 gallon of oil to 15 gallons of water. Or lime sul- phur may be used but, though it gives good control, it is being dis- continued on ornamentals because of the bad color it leaves and be- cause it is disagreeable to use. Spraving with oil for scale insects can MAR 26 1936 be done from February 15 to early April, as weather permits when the temperature is not below 35° F. Evonymus scale is similar in shape to oyster shell scale and is the most serious pest of Flvonymus, often killing entire brandies. There are at least two generations of these insects a year. Spray with mis- cible oil (l to 30) in the dormant season and again in summer when young scales liave hatched (l to 50). If the plants are badly infested a third spray may be necessary later. It is important to have the dor- mant spray weaker than for other scale insects, on account of ever- green foliage of Evonymus radicans and its varieties. Considerable damage is done to pines and spruces by the pine-leaf scale which is easily recognized because it gives the trees a whitish appearance. Spray with miscible oil early in April, 1 part oil to 30 parts water. Spruce-gall aphids can be easily recognized by pineapple-shaped galls on new growth of spruce trees, native and foreign. These gall growths are caused by small whitish plant lice feeding at the base of the leaves of young shoots. In August these galls become yellowish, dry and open, and the winged lice escape. Spraying in early spring before the new growth starts (about the middle of April) with misci- ble oil, 1 part miscible oil to 30 parts of water, will aid materially in controlling this pest. The work of the larch case-bearer is easily recognized by the leaves of the larch turning yellow or brown in early spring. This injury is caused by the feeding of a brown, black-headed caterpillar about I inch long, first biting a hole (in the leaf) and then mining in the leaf. The caterpillar is enclosed in a small, grayish case. The young larvae at first mine in the larch leaf ; later, this is cut off and serves as a case for the larvae. The winter is passed in the larval stage in- side the case. We have found that early spring spraying with arsenate of lead, 2 pounds to 50 gallons of water when the young are feeding is an excellent method of control. Golden oak scale is one of the most destructive scales occurring on oaks. It can be easily detected as the scale is a beautiful, greenish golden color, and often kills twigs and entire branches. The scales pass the winter as almost mature individuals, the young emerging in May. The pest may be controlled by spraying in very early spring with miscible oil, 1 gallon to 15 of water. From the end of April to the middle of May, as new leaves appear, close watch should be given to canker-worms. As soon as they ap- pear spray should be applied at once as the.v cause considerable dam- [10] age in only a few days. There are two common kinds of canker-worms, one appearing in the spring, the other in the fall. The spring canker- worm seems to be the most injurious. It attacks maples, elms, oaks, apples and many other fruit and shade trees. The worms themselves are yellowish brown, about 1 inch long when fully grown. When crawling they arch the middle of their body, being a typical “meas- uring worm.” Spray should be applied when the worms are half grown, using arsenate of lead, ^2 pounds to oO gallons of water. In the past few years the willow leaf-beetle has been giving us con- siderable trouble. The beetle is a metallic blue in color, oval and rounded, about i of an inch long. There are two broods a year. It passes the winter under the rough bark of willow trees. Spray early in June with arsenate of lead, *2 pounds to 50 gallons of water. Great importance should be placed on getting the spray on the under sur- face of leaves, as the beetle feeds only on that surface. It is frequently so prevalent that it destroys all the foliage on certain species of wil- lows. Rhododendron lace-bug. The lace-bug does considerable damage every year to Rhododendrons and mountain laurels, producing un- sightly yellowish or brown spotting of the leaves, particularly on those in the full sun. It is a flat bug with light, lacy-like wings. I'he insect overwinters in the egg stage along the midrib on the under side of leaf. These eggs hatch in the early part of May. There is also a second brood in August. Spraying with miscible oil, 1 to 70, as soon as they hatch will control the early brood. The under surface of the foliage should be sprayed very thoroughly, using Sunoco oil at the rate of 1 to 60, for the August brood does the most damage. Select a partly cloudy day with temperature not above 80° F. to prevent the burning of foliage. The elm leaf-beetle is one of the most destructive insects attacking elms. The beetles are about I of an inch long, yellowish green in color with a distinctly darker stripe along each side of the wing cases. J'he beetles pass the winter hidden under rougli bark and various other types of shelters. In the spring they lay their eggs on the under sur- face of the leaves of elms. The larvae, hatching from these eggs, feed on the under surface of the leaf and practically skeletonize it. Spray- ing in early June, or as the larvae appear, with arsenate of lead, S pounds to 50 gallons of water will control the beetle. This spray should be directed especially to the underside of the leaves. As there are two generations a year, a second spray is necessary by the middle of July. [11] Rusty colored evergreens in summer often indicate red spider in- jury. These pests multiply very rapidly during hot, dry weather. They can be controlled by spraying with Sunoco oil, 1 gallon to 100 gallons of water, on a partly cloudy day with the temperature not over 80° F. We obtain best results in applying this as a very fine misty spray, using considerable force. White pine weevil has caused considerable damage to young white pines in the Arboretum. It is easily determined by the central or ter- minal leader wilting and turning brown. As this damage is caused by grubs within the wood it is very hard to control. Cutout brown lead- ers and shoots at least several inches below the point where browning first occurs. There are several borers that cause considerable damage to shade and fruit trees. Round-headed and fiat-headed apple tree borers have long been a problem on fruit trees. The work of these borers is in- dicated by shallow burrows on the main trunk just under the bark. Some are noticeable in the spring by the fresh dust or burrow exca- vations on the trunk. The most effective way of controlling these grubs at the Arboretum has been to cut them out with a sharp point- ed knife. Leopard moth attacks a number of our valuable shade trees such as elms, maples, and lindens. These insects take 2 or 3 years to de- velop, so that two or three winters are passed in the larval stage. Young trees should be watched as borers get into the main stem. When a hole is located the grub can usually be hooked out with a wire. If this is not successful, put a few drops of carbon bisulphide into the hole and then putty up the opening. Again we repeat that these control methods are the ones which are actually being used successfully at the Arboretum and have been for several years. However, there are other materials and possible other methods of control which would probably prove just as satisfactory. L. V. Schmitt [1-2] Note, in all cases where miscible oil is recommended in this bul- letin, such recommendations have been based on Sunoco oil only, which has proved satisfactory at the Arboretum. There are several books and bulletins available as references for problems dealing with insects or diseases. A few of the outstanding ones mio^ht be : Britton, W.E. Plant pest handbook for Connecticut, i. Insects. New Haven. 1933. Connecticut aofricultural experiment sta- tion. Bulletin, 344. Chambers, E. L. and Thompson, N. F. Pests and diseases of trees and shrubs. Madison. 1933. Wisconsin department of agriculture and markets. Bulletin, 145. Clinton, G.P. Plant pest handbook for Connecticut, ii. Diseases and injuries. New Haven. 1934. Connecticut agricultural ex- periment station. Bulletin, 358. Felt, Vj. P. and Rankin, W. H. Insects and diseases of orna- mental trees and shrubs. New York. 1932. Macmillan Com- jjany. Herrick, G. W. Insect enemies of shade trees. Ithaca. 1935. Comstock Publishing Company. Wilson, Andrew. Insects and their control. New Brunswick, N. J. 1929. Thatcher-Anderson Compaii}'. [13] SPRAY PROGRAM AT THE ARNOLD ARBORETUM Spray Amount When Material to Apply to Apply Scale insects Miscible oil 1-1.5 Feb. 1.5 to early April Evonymus scale T T o o when plants are dormant in the summer Pine-leaf scale T o early April Spruce-gall aphids “ “ 1-30 April 15 Larch case-bearer Arsenate of lead *2 lbs. -.50 gal. when young are feeding Golden oak scale Miscible oil 1-1.5 early spring Spring canker-worm Arsenate of lead lbs. -.50 gal. as soon as young appear Willow leaf beetle “ “ “ 2 lbs. -50 gal. early June, applied to un- der surface of the leaves Lace-bug of Rhododend rons Sunoco oil 1—60 as they hatch in the spring in August on a partly cloudy day when the tem- perature is not over 80° F. lL,lm leaf-beetle Arsenate of lead 3 lbs. -.50 gal. early June. A second spray may be necessary for a second brood Red spider on evergreens Sunoco oil 1 — 100 applied in summer as a fine mist on a cloudy day when temperature is not over 80° F. White pine weevil cut out borers and dead liranches Borers dig out L. V. Schmitt [14] ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV APRIL 1, 1936 Number 3 THE VIEWPOINT OF THE ARNOLD ARBORETUM ON THE DUTCH ELM DISEASE MONO the various problems in the conservation of tree life in the United States the Dutch elm disease takes precedence. It is the most urgent because the Dutch elm disease is potentially cap- able of destroying practically all of our elms so long as it remains within our borders and because, failing intelligent, persistent, ag- gressive action, the time that remains to us during which we still re- tain the power to get rid of it is uncertainly and perilously short. The question before us is how best can we continue to meet the problem. From the outset the Arnold Arboretum has advocated complete erad- ication of the Dutch elm disease from the United States as the guid- ing principle, for, after due consideration of its nature and its means of spread, no other measure seemed to offer any hope if our elms were to be saved. Added knowledge and experience during the ensuing years have but served to strengthen our earlier convictions. So, in considering future action, we continue to unreservedly support the policy of eradication, with its complement of sanitation, which has been sponsored by the Federal Government and facilitated by State cooperation. Indeed, we are more strongly convinced than ever that it offers the only chance of preserving the priceless national heritages, the retention of which is at stake — our American elms of all species. 'I'he federal machinery for combating the Dutch elm disease, asset up in 1933, consists of- (l) a laboratory at Morristown, N.J., for di- agnosis arftl research ; (s) offices at White Plains, N.Y., East Orange, N.J. and Stamford, Conn, which are responsible for (a) scouting, (b) eradication, (c) elm sanitation and (d) technical and educational projects. Organized cooperation, in addition, is afforded by the States [15] in which the disease is known to occur. The actual workinjr of the machinery has been as follows. The in- fected area and a surrounding 10-mile zone have been mapped and divided into administrative units; each unit is methodically scouted during the growing season in search of trees that exhibit suspicious symptoms ; specimens from these trees are sent to the Morristown laboratory for diagnosis; if the diagnosis reveals the disease, the trees involved are condemned ; the condemned trees are then promptly cut down and burned. Throughout the year a sanitation corps is occupied with a systematized removal of dead and decrepit elms within the af- fected area regardless of whether or not they carry the Dutch elm dis- ease fungus ; the purpose of this is to destroy the breeding places of the insect carriers and accessory breeding places of the fungus. Additional important service is rendered by the Morristown laboratory by re- searches that are designed to afford extended knowledge of the dis- ease and its means of spread. Speed in the detection and removal of diseased trees is of great importance, because such trees are not a menace in the spread of the disease until the * ‘carrier” insects have had a few weeks in which to breed in the decrepit stems and branches. It should be added that continuity of the eradication service over a period of years is obviously of paramount importance because of the fact that several years may elapse before symptoms appear in an infected tree. But by dogged persistence the number of cases can surely be reduced to zero, just as has been true of an eradication campaign against citrus canker in Florida. Beginning there in 191.5, at which time canker was present in ‘26 counties, the last diseased tree was found in 19^27, and no in- stance of citrus canker in Florida has been found since that time. Up to the summer of 19.S5 deductions as to the probable success of this policy were based solely on biological data derived, mainly, from European investigations ; no practical tests of its efficacy had been previously made anywhere. Not until the fall of 1934 had a compre- hensive survey of the range and the intensity of the occurrence of the Dutch elm disease in America been completed ; and not until the spring of 1935 had those trees in which symptoms had become mani- fest been cut down and burned. With the compiled experiences of 1935 now available, however, we have, for the first time, statistical data against which to check our theoretical conclusions. It will, I think, be generally agreed that in discussing these data we may dismiss without further reference the single, small infection spots respectively in Virginia, Maryland, Indiana, northern Connecti- [1(5] The Old I^andcaster Kliii Courtesy of the Massachusetts Forest and Park Association cut, and the two small spots in Ohio. All told they have involved fewer than 4-0 trees; the situation in each has been, and is beinjr, closely watched and is well in hand. Moreover, exce{)t for Old Lyine, Connecticut, the origin of the infections in these locations is known with reasonable certainty and suitable restrictions on importations have been enforced by the Federal Quarantine Office to guard against the likelihood of further new outbreaks. Our main concern is with the infection area radiating out about 4-5 miles from the port of New York, an area embracing contiguous portions of the states of New York, New Jersey and Connecticut. The results of the work of eradication and sanitation in this New York area, as revealed by the compilations of 1934 and 1935, afford great encouragement. Certainly a good beginning has been made to- wards the objective. Thus the number of trees showing symptoms of the disease appears to have been somewhat fewer in 1935 than in 1934 — in round numbers for 1935, say 6,700 trees, that is, less than one-half of one percent of the elm population of the area involved. What a contrast with the doleful efforts to get rid of the chestnut blight! Then, too, the condemned trees were cut down and destroyed so promptly in 1935 that probably comparatively few of them were factors in a continuation of the epidemic. It is just in that feature, too, that the sanitation program helps enormously. Again it is highly significant that scarcely a dozen infected trees were found in the sur- rounding 10-mile scouted zone^ — a zone tentatively regarded in 1934 as infection-free. How many of these were really infected before the eradication project was begun, in other words, how many were really new cases, is purely a matter of surmise. The same question arises with all the other cases found in 1935. This uncertainty is obvious when we remember that the disease may be present in a tree for five years before external symptoms are manifest and that our acquaintance with it in the New York area covers a period of less than three years. As for the sanitation project, hundreds of thousands of dead and mori- bund elms have been eliminated — a very impressive step towards the goal of utterly removing the breeding places of beetle agents pre- ponderantly responsible for spreading the disease-producing fungus. Taking all these facts into consideration my own opinion of the re- sults of the eradication work to date is that they indicate a substan- tial reduction of the disease in the New York area. At the very least we can confidently assert that combined Federal and State efforts have apparently held the disease in check and greatly lessened its po- tential spread. Surely there is good reason to conclude that we prob- ably can save our elms if we will, and that the cost of the elfort will be vastly less than that of removing dead trees if the disease be al- lowed to take its course. Further evidence of the success of our eradication policy is afforded by comparing the status of the Dutch elm disease situation in Amer- ica with that of western Europe — a region in which eradication has not been attempted. This will also help us to visualize the anticipated fate of our elms if we do not or cannot eradicate the Dutch elm dis- ease. A few extracts from two recent reports (l93o) which we owe to the British Forestry Commission will suffice to give us the picture. Quoting — *^In Utrecht 64% of the elms have already been removed, in Rotterdam 55%.’* ^^Between Louvain and Diest, a distance of ^28 kilometres, there was originally a more or less continuous avenue of elms, about ! of which have been felled as a result of the disease, and about 3 of those remaining are dead.” *‘This is comparable to the Newport Bishop’s Stortford area in England.” An estate in Worces- ter, England, ‘Reports that 500 elms are to be felled in 1935 owing to the disease.” As for England the British Forestry Commission finds **it is still impossible to recommend the planting of elms.” As for Holland **it is assumed that all the present stand of elms in Hol- land, with the exception of a few specimens of resistant varieties, will eventually succumb to the disease.” In other words, the elm situa- tion in western Europe appears to be hopeless. The conclusion is surely inescapable that, unless eradicated, the Dutch elm disease is not likely to be less disastrous in America than it is proving to be in Europe, knowing as we do from repeated tests that American species of elms rank among the most susceptible of all elms. And now let us turn briefly to the question of costs. That matter must be faced regardless of what is done about our elms, whether we try to save them or leave them to their fate. It may readily be ad- mitted that considerable cost will be incurred in carrying through the eradication project because it will take several years to bring it to completion. But costs are sure to be many, many times greater if we do not eradicate the Dutch elm disease. To my mind there is no al- ternative. So-called * ‘control,” short of eradication, may defer the loss of our elms; but the conclusion in Holland, where essentially such a measure is being practiced, is that the elms will eventually go. Actually such “control’* may be more costly in the aggregate than doing nothing at all. If our elms be allowed to die there will be un- avoidable costs of removal and these will be huge because of the vast number of trees involved. Then there will be costs of replacements, losses of property values, and the sad loss of the American elm for planting — a tree for which there is no equivalent. In conclusion I should refer to criticisms that have been expressed with regard to certain practical features in connection with the carry- ing out of the eradication and sanitation programs. Fortunately, so far as I know, none have had reference to the scientific staff or the administrative officers in charge. We express complete confidence in them and admiration for what they have accomplished. There have been two serious criticisms : delays in making appropriations available, and insistence on employing a large proportion of field workers with- out due regard to their efficiency and training. Both procedures threat- en the success of the undertaking, either through the chance that the area of infection may in consequence become so extended that eradi- cation will be impossible of accomplishment, or through the danger that the process will be so long protracted that the people will tire and then withhold appropriations. Both can be corrected. It is plain that not only should appropriations be adequate but also that they should be available when best use can be made of them. They should be included in the regular budget, and the logical unit to handle this work would seem to be the Department of Agriculture. It is equally plain that the administrative officers should be made responsible for the efficiency of their field forces, which, of course, is irrational un- less they are empowered to choose workers of the type needed. Notwithstanding these criticisms the Arnold Arboretum holds fast to the adopted policy of eradication and its attendant sanitation pro- ject. The ship may leak somewhat at present, but the leaks can be mended. We have confidence that they will be and that the ship will, if there be no sabotage, reach its planned destination. Our confidence is strong because Ave believe the United States has begun its campaign in time. We knoAv the locations and the extent of infected areas: and their size is not yet baffling. Of great importance is the circumstance that Ave are acquainted AA'ith the essential scientific aspects of the dis- ease : from them Ave judge that it lends itself ideally to eradication. Moreover, from the practical results attained Ave believe the sound- ness of the policy has been demonstrated. It looks as though it offers the AA'ay out and at minimum costs. We are firmly convinced that the preserA'ation of America's elms for our own and succeeding genera- tions lies in our oAvn hands. But there must be unflagging persistence and continuity of endeavor. Our purpose can be attained if Ave ex- press an interest that Avill command the leadership and basic support of Congress. J. H. Faull THE LODER RHODODENDRON CUP The Arboretum is justly proud of the fact that the Loder Rho- dodendron Cup has recently been awarded to Professor Alfred Rehder for the year 1986. This makes the third time the cup has been awarded outside England, and each time it has come to men on the staff of the Arnold Arboretum. In 1924 it was awarded to Pro- fessor Charles S. Sargent, in 1927 to Dr. E. H. Wilson, and in 1986 to Professor Rehder. I'he Loder Rhododendron Cup is awarded by a joint committee of the Royal Horticultural Society and the Rhododendron Society to men who have been outstanding in promoting knowledge concerning Rho- dodendrons. It vv^as donated in 1921 by Mr. G.W.E. Loder in mem- ory of his brother. Sir Edmund Loder. Professor Rehder has for many years been making valuable contri- butions to our knowledge of Rhododendrons. Two notable examples are his contributions in “The Species of Rhododendrons,” published by the Rhododendron Society of London, and “A Monograph of Azaleas” by E. H. Wilson and Alfred Rehder. ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV APRIL 6, 1986 Number 4 EARLY BLOOMING SHRUBS AT THE ARBORETUM WITCH-HAZELS. These plants afford a **tie in” with fall and springy. The common witch-hazel virghiiano) is the last plant to bloom in the fall, usually late October or November. The vernal witch-hazel is the first woody plant to bloom in the spring at the Arboretum. This year some of the plants were in bloom by the middle of January. Hamamelis japonica and H. mollis bloom later in February or March. This year they both started about March 15. The leaves of the Japanese witch-hazel {H . japonica) have a bril- liant scarlet to orange autumn color, while the foliage of all the others are colored a good yellow in the fall. Though there are many plants with yellow colored foliage in the fall, these witch-hazels can alwaj s be counted on to be outstanding. Hamamelis virginiana is a more or less scraggly growing plant, which is native all through the northeastern United States. In fact, it is much better used in naturalistic plantings and along the borders of woods than elsewhere because of this loose habit of growth. Hama- melis vernalisy native to southern Missouri and adjacent regions, was first brought to the attention of gardeners by Professor C. S. Sargent about 1908. It grows 5 to 8 feet tall, is dense and suckers very much at the base, making it an excellent species to use in mass plantings. It is the most floriferous of all the witch-hazels, though the individual flowers are the smallest. Therefore it is not as showy as the two Asi- atic species, but it is valued for its fragrance, the flowers having a very distinctive and aromatic odor. There is a rather wide variation in the time individual plants bloom and in the color of the flowers. 'Fypically, these have yellowish petals which are reddish towards the base, riie flowers are closed when the temperature is low, and then [ -2:5 ] 1936 the petals ijradually expand wlien it jjets warmer, a very interestintj process. llamamelis jnponica^ the Japanese species, is similar in habit to H. virginidua , but the Howers are larger and more plentiful. The petals are pure yellow while the cupped sepals are more or less purple on the inside. J'he variety arhorea is more tree-like in form with golden yellow petals, calyx deep purple on the inside, and the stamens with purple anthers. The other varieties, H.japouica Jlavo-purpurascens and H. japonica Zuccariniana^ are apparently just as hardy, the former being of more ornamental value because of its larger red and yellow flowers. As a rule it is hardier than H. mollis. The Chinese witch- hazel [H. mollis) is the one that has the largest and the most con- spicuous flowers of all and has been the most publicized. Unfortu- nately, it cannot always be depended upon at the Arboretum. The flowers, and even the flower buds themselves, are subject to injur.v from low temperatures, and none of the plants at the Arboretum have given a good performance during recent years. In warmer sections, or in places where this plant can be given ample winter protection, there is no doubt that it is an addition to the garden, particularly since it is the most outstanding of the small group of plants in bloom at this time of year. Daphne species. The February daphne {Daphne Mezereum) is the most common of this group, since it has become naturalized at various places in the eastern United States. It is a nativ e of Europe and has been in cultivation for about four hundred years. This is another plant whose early, fragrant, purplish spring flowers (there is a white flow- ered variety also) are not noticeably affected by freezing. When plants bloom at this early time in the year they are subjected often to vio- lent changes in temperature, and the only flowers of value to us then are those which can stand such conditions. February daphne has red fruits in the summer, and these, combined with the green color of the leaves make a very effective combination at that time. I'he lilac daphne (D. genkmi) , though it has pretty violet colored blossoms, yellow fruits, and blooms in early May, has not proved very satisfactory here at the Arboretum. It has previously been grown here, but every now and then is either completely killed or is given a severe setback by a cold winter. This plant may do better further south, but cannot be recommended for climatic conditions similar to those at the Arboretum. Daphne Cneorum blooms in mid-May. There are three other members of this genus, all of them white- flowered, which have been grown at one time or another at the Arbo- Haniamelis mollis H. japonica H . japonica Zuccariniana H. vernalis return. They are D.altaica^ D.caucasica and D.alpina^ none of wliieh are particularly outstandinjj. The Cornelian Cherry iCoruus mas). A native of southern Europe and western Asia, this plant has been used in jjardens for over three hundred years, and in this country for over a century. It is of value chiefly for its very early, brijjht yellow flowers, which apparently are not injured by late freezes. The flower buds themselves can usually be counted on even duringr the coldest winters in this section of the United States. It blooms at a time when there is little else of impor- tance in flower except the early species of Hamamelis and Daphne Mezereum. Added to its effectiveness of flower is the beautiful, rich, dark orreen, shiny foliage, which is attractive all summer long. The fruits are something like elongated cherries, ripening during the sum- mertime, red in color, and in Europe often used for making preserves. The plant itself is vigorous, dense, and is even used for clipped hedges, though it would be better perhaps to use it as an undipped windbreak. Th ere is a yellow-fruited form growing at the Arboretum. The amount of fruit it bears apparently depends on weather condi- tions, for when the weather is particularly cold at blossomtine, there often results a very small amount of fruit later. The Japanese cornelian cherry iCornus officinalis) is very similar from a horticultural standpoint. It, however, is native of Japan and has only been in this country about sixty years. There is a striking dif- ference in the bark of these two plants, in that the bark of C. mas is very close in texture, and a dark grey, while that of C. officinalis is loose, splitting and peeling off on the second and third year’s growth, into short, papery strands. It is reddish brown in color. From a horti- cultural standpoint one of these plants is practically the same as the other. They are both valued for dependable early flowers, good foliage and fruit, and a good dense habit of growth. Blooming periods. It is difficult to predict the weather conditions very far in advance, but it may be interesting to some if we list a number of the outstanding groups of plants, together with the ap- proximate time that they normally would be expected to bloom. Middle April — Forsythias Late April^ — ^Single flowered forms of Japanese cherries Early May — Shadbushes, Japanese quinces, early spiraeas Middle May — Crabapples, double flowered Japanese cherries, red bud and flowering dogwood Late May — Lilacs, wisterias, deutzias, diervillas, hawthorns Donald Wvman ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4-. Vol. IV APRIL 13, 1936 Number 5 PLANTS BLOOMING IN APRIL AND SOME MAGNOLIAS PIERIS FLORIBUNDA. The mountain andromeda has always been dependable at the Arboretum, much more so than the rho- dodendrons. Professor Sargent wrote of it that, **judging by an ex- perience of over fifty years, it is the only broad-leaved evergreen to which nothing ever happens in this climate.” It is not attacked by borers or the lace wing-fly, so troublesome on rhododendrons; its fol- iage stays a good bright green all winter long, and its nodding clus- ters of white flower buds are rarely injured by winter cold. They open the first thing in the spring and are in bloom now at the Arboretum. The mountain andromeda can not be recommended too highly, and, fortunately, is being used more frequently as its good properties are recognized. Pieris japonica, the Japanese andromeda, is considerably less har- dy, though its dark, shiny green leaves and the greater height to which it grows make it the more handsome of the two. However, there are some protected places in eastern Massachusetts (and at the Arboretum) where it is doing well ; its clusters of flower buds hanging on the plant in graceful, drooping {lanicles, and its white flowers are certainly an asset in the garden at this time of year, if they can be brought through the winter uninjured. The Corylopsis, now in bloom, are oriental shrubs, very similar to the witch-hazels in general habit. All species have yellow, drooping spikes of flowers before the leaves open. There are three Japanese forms, the oldest in cultivation being Corylopsis spicata and C. pauci- Jiora. Unfortunately, these two plants can not be depended upon at the Arboretum, for they are frequently injured in the winter; either the flower buds themselves are killed or the branches and twigs are iPE 161936 killed hack severely. I'lie liardiest species is C.glabrescens (formerly C. Gotoana) which is, unfortunately, not very eoinmon in the trade. Seeds of this species were first sent to the Arboretum from Korea by Professor J. G. Jack in 1905, and the plant itself has proved the hard- iest and handsomest of the lot. Thoufjh the buds have been occa- sionally injured in the winter, such injury has never been as severe as that of the other species. It throws as much as 10 feet in height. The two Chinese species, C. Veitcfuana and C. WillmnUiae^ have been killed repeatedly at the Arboretum and are not recommended for this region. Rhododendron dauricum mucronulatum. Thougrli this * ^Azalea” was discovered in the mountains west of Pekin‘S in 1835 by Dr. P.V. Kirilow,it was not introduced to America until Dr. Emil Bretschneider sent seeds to the Arboretum in 1882. The flowers of this variety are laro^e, rosy purple and not nearly maarl y-ll<)weriMj>' llluxlodendroM (ddurlrtim vJir. murromdul nm) ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV APRIL 27, 1936 Number 6 EARLY JAPANESE CHERRIES, THE QUINCES AND SHADBUSHES Actually, the first Prunus to bloom at the Arboretum is Prunus Davidiana (starting this year on April l) and followed by P. mandshurica the middle of the month. In New York and New Eng- land Japanese cherries begin to bloom usually the latter part of April and by the time this Bulletin reaches its readers the early, single fiowered group of these cherries will be in full bloom. Sargent’s cherry, P. Sargentii, formerly P. serrulata sachalinensis , is the hardiest of these flowering cherries. It grows to be a standard tree, has light pink flowers, and the young foliage as it unfurls is a good bronze color, an excellent combination. Since the flowers are single, it, un- fortunately, does not hold them very long, particularly during warm spells. Prunus subhirtella is admittedly the most floriferous of any of this early flowering group, frequently having so many flowers that trunk and branches are actually hidden. The flowers are single, light pink. The tree itself is usually small and bushy, and among seedlings, there is considerable variation in the form of dift'erent plants. Its weeping form, P. subhirtella peudula, is now common everywhere, and was very likely one of the first ** Japanese cherries” introduced into this coun- try. In 1846 the old Ellwanger and Barry Nursery of Rochester, New York, listed a plant in their catalogue at that time, which was un- doubtedly this variety. The Yoshino cherry, J\ yedoensis, is a beautiful tree with single white flowers, blooming just a few days later than the Sargent cherry, and which is slightly flower bud tender during the severest of New England winters. Where it succeeds, it makes an excellent cornbina- [31] APR 281936 tion with the deep pink-Howered P. Sargentii. It is interesting to note, that in the ori«rinal nfift of over two thousand cherry trees from the city of Tokyo to the city of Washington, in 191*2, this tree constituted about lialf the lot. In fact. Professor C. S. Sartjent in writing about the Yoshino in 19*2*2 said that, prior to the ^reat earthcjuake, there were at least two hundred and fifty thousand of these trees ijrowinjj in Tokyo. This shows what the Japanese think of this beautiful tree. These four trees then constitute the most outstanding of the single- flowered types, all of which bloom at about the same time. After this group has passed the stage of full flower, the double-flowered forms start to bloom, led by the Naden cherry, P. Sieboldii. Japanese Quinces. There has been a great confusion about the nomenclature of this group of plants, but in common parlance they can still be termed Japanese quinces. Chaenomeles lageuaria is the scientific name now given to the old-fashioned Japanese quince for- merly called Chaenomeles japonica or Cydonia japonica, which used to be planted so frequently for hedges before the advent of Japanese barberry. It was introduced from Japan, possibly before 1800, and is still a garden favorite. It will soon be in full bloom at the Arboretum. Since it has been in cultivation so long, there are naturally various varieties, with flowers of different hues, and some even with double flowers. Since many of these varieties are in the trade, but are only offered under the species name, it would only be confusion to mention them here. Suffice it to say that there are varieties in white, pink, a rich dark red, and various combinations of these. The true Chaenomeles japonica {Cydonia Maulei now in the trade) is a lovely little plant which should be better known. It is not as tall growing as Chaenomeles lagenaria, seldom getting more than t2 or 8 feet tall, but is dense and compact with some varieties of very bril- liantly colored flowers. Since these flowering quinces, together with the common quince, Cydonia oblonga, which has little ornamental value but is used con- siderably for its fruits, are all members of the apple family, they are, of course, all subject to fire blight, borer and scale, and perhaps this is the chief reason why the Japanese barberry has replaced them in hedge plantings. The Shadbushes. Now the shadbushes will soon be in bloom all over the northeastern United States. Often called shadblows, ser- vice berries or Juneberries, they are so named because they bloom at about the same time the shad run up the streams from the sea; their edible fruits ripen in June. There are tree types, Amelanchier cana- Japanese wSpring' Cherry {Prtniu.s tmbhh'tcHa) densis, A. laevis and A. grandiflora, and bushy types, A. ob/ongifo/ia and A. spicata. Their delicate white Howers, common to everyone familiar with the woods at this time of year, are all practically the same from a landscape point of view with the possible exception of A . grandiflora (A. canadensis X A. laevis) which has the largest Howers of any. Its variet.v, rnhescens, has Howers which are more or less tinjred with rose. Sometimes, unfortunately, weather conditions are such that the plants are only effective in Hower for a very few days, par- ticularly when a rather long cold spell has kept the buds from open- ing, followed by a sudden warm spell during which they open with a rush. It seems worthless, often, to use plants for only a few days effectiveness in the year, but the Amelanchiers have the added ad- vantage of beautiful gray bark, and a fairly good autumn red color, together with fruits in June which are attractive to birds. Amelanchiers are most effectively used in naturalistic plantings, es- pecially on the borders of woodlands. Their dainty white blossoms, open now, seem to be a fulfilled promise that spring has come at last. Immediately after they are through blooming a great majority of plants burst out into leaf. Early Spireas. Two of the first Spireas to bloom in the spring are Thunberg’s Spiraea Thnnbergii, and bridalwreath, .S', prunifolia plena. Both these plants may be somewhat tender in New England, but in other sections they are both very common. Since Thunberg's Spirea is the first to bloom, it might be used effectively with the pink Prunus triloba plena, now in bloom. The double-Howered bridalwreath on the other hand can be used very effectively with the lower growing and later blooming pink-Howered Prunus gland ulosa sinensis. In planning or replanting shrub groups enough emphasis cannot be placed on this very important factor of flower color and blooming dates, since effec- tive combinations like these are decidedly worth while. Other Plants Now in Bloom. With the early warm spell this spring and the more recent cold rainy spell the blooming dates of plants are again back to normal. Plants in bloom at the Arboretum now are the Corylopsis species, the forsythias, Cornus mas and C. officinalis, though these are about past, Dirca palustris. Benzoin aestivale, Acer rubrum, Prunus mandshurica. Erica carnea, Pieris floribunda. Vinca minor and Magnolia stellata, though M. denudata, M. kobus and even some of the M. Soulangeana varieties are fast nearing full bloom. Though it is hard to gauge blooming dates, particularly this year, we hazard a guess that the crabapples will be at their height of bloom May 10 to 16. Lilacs will probably be best at about May 15 to ‘20. Donald Wvmax [34] ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV MAY 9, 1936 Number 7 THE FLOWERING CRABAPPLES At this time of year in New England and New York, the flowerino^ crabapples are in full bloom. Collected from widely segregated places in the northern hemisphere, nurserymen in this country are able to offer over fifty of them to the public. Generally, they can be grown wherever the common apple does well as far as hardiness is concerned, and, though subject to similar apple troubles such as borer and scale, they are an asset to any garden. The sizes and shapes of the twenty-six different crabapples listed in this bul- letin differ greatly. Mains haccata mandshurica is not only the first to bloom, starting this year while the Japanese cherries were still in flower, but is also the tallest, growing to fifty feet or more. On the other hand. Mains Sargenti is the smallest, often growing twice as broad as it does high and seldom becoming over 8 feet tall. This might be the best crab- apple for the small home garden where space is the limiting factor. Unfortunately, nurserymen often grow it from seed which has not been collected from pure stands, resulting in trees that do not have the typical low-growing habit but are much more upright. Since there are few, if any, pure stands in this country, grafting might better be resorted to in order to insure the typical form. The rest of the flow- ering crabapples range in height from lo to 30 feet, the majority of them being 15 to 25 feet tall. Some, like M. Halliana Parkmani, rarely exceed 15 feet, while others like M. ioensis plena and M. jlorihnnda may attain 30 feet. Some of the varieties, like M, prnni folia rinlci, are upright and spreading in habit of growth ; others, like M. Jlorihnnda and M. arnoldiana , are generally mound-like in appearance. I'he most picturescpie in habit is the tea crab, now called A/, linpeliensis, but [ 3o ] 181925 listed in nursery eatalojjues as M. theifera. I'he main branelies, orig- inating from the trunk, are long with few side branehes, appearing from a distance somewhat like a huge fan. Like the common apples, the flowering crab has a strong tendency to be alternate bearing, that is, fruit production is poor one year but good the next. I'hough this may not be particularly noticeable in the flowering, it is very noticeable and often disappointing in the fruiting habits. For instance, the best fruiting tree in the group at the Arbo- retum (3/. toringoides) was marvelous in fruit during the fall of but last year, even the largest plant was uninteresting because of few fruits. The Asiatic crabapples (see table) are the first to bloom, followed shortly afterwards by the native species. The flower display lasts about a week, but, of course, depends entirely upon the weather, and this year is somewhat advanced because of the recent unusual warm spell. When this issue of the Bulletin reaches its readers the crabapples will be in full bloom at the Arboretum. Some years when the weather is particularly cool the beauty of these plants is prolonged, for some of them as, for instance, M. hupehensis (M. theifera) are often considered more beautiful when the flower buds are fully advanced but not open, than when they are in full bloom. In extremely hot weather plants may drop their petals two or three days after the flowers expand. In new England and parts of New York, the past few winters have demonstrated that it is not worth while to count on the hardiness of the double-flowered Japanese cherries. Garden lovers in general should realize that the crabapples are considerably hardier and that there are also double-flowered forms (see table). Though these may not be con- sidered as worthy substitutes for cherries, they can at least be counted on to bloom. The least hardy of all the crabapples is the Parkman crab, 3/. Halliana Parkmani, which was injured considerably during the winters of 1933 and 1934, both in New York and at the Arboretum. The method of propagating these plants varies considerably. Many of the species can be easily grown from seeds, but in botanic garden collections, where a number of species are in close proximity, there is ample opportunity for cross polliniation ; and it has been definitely proved that 3/. Sargenti when grown from seed thus collected does not give plants with the desired low-growing habit but rather plants with a more upright form. It is much safer to bud or graft all forms, ob- taining buds or scions from stock plants with known characteristics. There is a confusion in the nomenclature of the crabapples in many nurseries today, simply because large scale production from seed has resulted in many variations from true types. Asexual reproduction naturally brings up the problem of under- stocks, which is by no means definitely settled. The American species are best grafted on seedlings of M.ioensis or M.coronaria. Both French crab seedlings and those of the various Asiatic species have proved successful for the Asiatic forms, especially M. rohusta. Crabapples are hosts of Juniper rusts, and the Arnold Arboretum has found the Asiatic species to be the least susceptible. There are places around Boston where Bechtel’s crab becomes so disfigured with this disease that it is not grown. Bordeaux has been used in efforts at control but apparently the disease thrives on it. After several years of careful investigation, the Arnold Arboretum recommends the fol- lowing for its perfect control on ornamental flowering crabapples : Use 5 to 6 pounds of “Linco”, a colloidal sulphur spray produced by the Mechling Chemical Company, Canton, New Jersey, with 100 gallons of water with 3 pounds of ‘*S. S. S.”, a commercial ^ ^spreader” a- vailable at any store selling spray materials. Spray at first when the young leaves become visible and follow with four or five sprays at six to ten days intervals. Spraying just before a rain gives optimum re- sults. To control chewing insects, add 4 pounds of lead arsenate to one of the later applications. Plant Accessions. During the past summer, Mr. W. H. Judd spent considerable time visiting European nurseries with the object of add- ing to the living collections at the Arboretum. Due to his efforts over four hundred different species and varieties of living plants have been added to our collections this spring. Then, too, nurserymen in this country have been generous in sending the Arboretum specimens of new things so that additional plants from this source number over one hundred. Cuttings, scions and seeds, received from various sources this spring, will add still another hundred species and varieties to our collections. A list of the nurseries sending material is as follows: Berlin- Dahlem Botanic Gardens, Berlin 4 L. Spaeth, Berlin *24 H. A. Hesse, Weener-Ems, Germany 1*26 V. Lemoine & Cie, Nancy, France J3 Vilmorin, Verrieres, France 10 Moser ik Sons, Versailles, France 14 Leon Chenault, Orleans, France 33 Hillier & Sons, Winchester, England 30 Royal Botanic Gardens, Kew, England 80 W. J. Marehant, Wimborne, England 13 Joseph \V. Gable, Stewartstown, Pa. 10 New York Botanic Garden, New York '25 Bobbink & Atkins, Rutherford, New Jersey 1 Hujjh Barclay, Narberth, Pa. 4 Boyce Thompson Institute, Yonkers, N. Y. 13 Bristol Nurseries, Bristol, Conn. 2 Linn County Nurseries, Center Point, Iowa ^2 United States Department of Agriculture, Washington, D.C. 15 Wayside Gardens, Mentor, Ohio 1 Mt. Desert Nurseries, Bar Harbor, Maine 2 Princeton Nurseries, Princeton, N. J. 23 Dr. Emmet Rixford, San Francisco, California 12 Winter injury at the Arboretum this past winter has been surpris- ingly small. Though certain plants have been affected they normally suffer such injury every winter. It cannot be said that any plant or groups of plants have suffered here this past winter, other than the little normally expected. This may be partly due to the fine blanket of snow on the ground in the early part of the year, and the length of time it was effective. Even California privet and similar plants were not touched on the Arboretum grounds. The Field Class announced by the Arboretum some time ago, meet- ing Saturday mornings in May, has met enthusiastic response. Over fifty people were on hand for the first meeting. Plants now in full bloom at the Arboretum. This week and next the Arboretum is the most interesting of any time during the entire year because the most number of plants are in bloom. Most of the crabapples are at the height of bloom. Some Amelanchiers can still be seen here and there. Other plants in full bloom include Viburnum Carlesi, the various Cytissus, some of the Syringa Henryi varieties, Syringa oblata and its varieties, Caragana, Cercis canadensis and C. chinensis, Halesia species, Fothergilla, Daphne cneorum, some of the Spireas, the Pyrus group. Rhododendron schlippenbachi. Rhododen- dron 3'edoense poukhanense. Rhododendron obtusum Kaempferi and several others. Plants are looking in fine condition right now. Lilac Sunday at the Arboretum will be May 17. Donald Wyman [38] Mdlus iheifern = hupehensi.K ^Species native to the United States. °°“Asiatie Flowerinj^ ('rahapples' ' native to Asia. SI)=senii doni)le 0 0 0 0 0 0 0 c 0 0 0 s Ir y. X "x X X -c 'O a *0' x: ft 2 2^ p: 7q c 5 1 £■ 2 f4- Q 2. a "x — • a. a 2- E. 51 2 9: 55 z 2 2 ^ ^ ^ O o 2 2 n rz c 6 o » c o 2 c ft X X* X £L X •keri - - P5 2. ■ .ft • a- < a •-! X 1 • '2. • ?r B X - X • s ■ CIS . S . . S . . S . . S . ? - a - 2 A 'x> ^ = = ;c j: ^ S' 5' 7r ? r ^ X — X X X X X X X X ^ s. i - a 'c'c i -i-c*- 5: ^ 2. ^ 2 -• s. ?r =• a ^ 9 .r- “ zc' a J'- a ^ ^ ^ ^ -r 7 :;^ • ji a ft ft ft ft a ft ft ft a ft jq ft rt ft ft ft ft ft iq 0 0 X X X 1 X X X X X £! X X X X 0 0 X z X X X X X X 0 0 2- 2- 2. CL 2. 1 1 2. 2- 2- 1 1 CL 1 2- 2. 2. 2, 1 CL a a- S- ¥ a* "a 2* "n a- 'n 2" 2" 2* 2 2* to 0 __ to to „ _ _ — c 0: p 'vC oc — — — - S ■_ C: 2 O' O'. O'. to Of I' to C WF O-F to p p to *x *x "x 0-F o 5 a ft" ^ '■< o a ^ 5" 2- i o' . ^ '< 9- 2. 2: g, o 5^ CL 2 v; -s ►, 2^22 a- ^ CL CL Q o ■o -o ^ o o o o c o o o -t CL "1 ^ 8 8 8 CL CL CL ft o ^ a- =. 2 ^ 2- 11 El z '< = jq v; O, v: Vi ft 55 a ft — — 'C o 5; a ^ = • o 0“ o o' « :? « « o a- • iq jq tr -o I 8 § I c c d O o g £ 2 1 1 1 ^ 'r' to X X yi X X X 50 (O to XXX X X r." X 'O X to c: C to n: -a -■ O- Tq K 2. v; rt' C- ft Z 7q II 55 ca X Cl “O a o Z X - 2: X - X z 55 55 X 55 C. to c 2”. ir id rt; < < < 2 2 2 <->■ 2. E '2- rt- 0 0 C 2 B' Si rt B '1 •■< X 0 f o- 2- ^ o s ?r S '2- Cr- ^ ^ C ARNOLD ARBORETUM HARVARD UNIVERSITY •4^ BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV MAY 20, 1936 Number 8 JUST ABOUT LILACS Brought to this country by the earliest settlers, the lilac has endeared itself in the hearts of everyone. We cannot even think of a typical, old-fashioned New England garden without its lilac bush. Today gardeners have a list of twenty-eight different species and over three hundred different varieties from which to choose, truly a be- wildering number for the gardener who only has a small space and wants possibly only one or two of these lovely plants. This bulletin is written chiefly for those persons who want to know more about lilacs, their propagation, care and culture, but at the same time are only interested in a few of those which are best for ornamental use. It will be necessary to discuss briefly some of the more undesirable species simply for the record, because many people think that if a plant is unknown to them it is better than the ones they already have. It will be unnecessary to describe minutely all the species and va- rieties since there are other works in which this is well done. A se- lection will be made of what we think to be the best varieties, though it must be understood at the start that we fully realize this is a pre- carious thing to do. Every individual has his likes and dislikes, par- ticularly regarding plants. Sometimes we connect personal events with certain definite plants and for this reason these naturally are more important to us. All we can do here then is to offer a good selection of varieties in the hope that it will assist others in becoming more ob- servant in making their own selections accordingly. HISTORY Lilacs are not American plants. In fact, there is no member of this •renus native in the L’nited States, hut they were brouorht to this country by the earliest settlers from the eastern hemisphere. All of the species come either from Europe or Asia, except two from the islands of Japan. Introduced into cultivation before 1560. the old- fashioned lavender colored lilac {Syriuga vulgaris) and its white-flow- ered form have been crrown so lonor in cultivation that many variations have arisen From this early date, the hundreds of pink, red and deep purple-flowered forms have orraduall.v arisen and been carefully selected and propag-ated. The Persian lilac (.S', persica) is another plant that has been used almost as long as .S. vulgaris. It is interest- ing to note that this lilac, crossed with .S. vulgaris, gave the first hy- brid lilac to horticulture, the Chinese lilac (.S’, chinensis) . This origi- nated in the Botanical Garden at Rouen. France, about 1777, and has been also called .S. rothomagensis. The term “French hybrids” has been loosely applied to the large group of varieties of the common lilac, probably because so many of them originated in France. Victor Lemoine and his associates have been more outstanding in introducing varieties of the common lilac than any others. However, a great many horticulturists have worked with the lilac, carefully selecting plants in France, Germany, Belgium and Holland. Comparatively recently some of them have originated in the United States and Canada, where lilac enthusiasts like the late John Dunbar of the Rochester Parks, have spent years in careful se- lection of good flowering varieties. Besides the “French hybrids,** there are other species and varie- ties that have merit in ornamental plantings, some of which will be mentioned later. PROPAGATION The Arnold Arboretum is firm in its belief that lilacs are best on their “own roots”. This is a controversial point : it has been for some years and probably will be for some time to come. Lilacs do not root readily from cuttings. When grafted on privet or some other such stock they “take** quickly and get an early and vigorous start, but, as investigations in the Pathological Laboratory at the Arboretum have shown, they are subject to a severe disease known as the “graft blight” of lilacs. When this occurs the plant eventually dies. This disease most frequently occurs not in the nursery but after the plants have been in the garden for several years. There is little that can be done to cure the disease once it has become established in a plant. There are several ways of having own root** plants. One is to [40] C’oiifro, with flowers a f>:ood dark reddish purple, one of the best varieties of the eonimoii lilac. jrrat’t low down, atul place such plants lower in the soil than ordinarily so that eventually the {rraft union is about 4- inches below the soil level and then the scion will throw out roots itself in from two to four years. Eventually then, the privet portion could be cut olf‘. This sounds easy but varieties differ f^reatly in the rapidity with which they make their own roots, this beinjr a constant difficulty to nurserymen. Lilacs may also be Q s 5 .o < Ct, C/D U u u C/D H -Si C/D H CQ x U X H j= "a o ^ 'O c ^ ^ S £ -t: o O ^ 5 w ^ B :5 e ^ •=1 3 ^ -c a ^ .a a 0) 3 XI :z X - 3 0® :c cj 2^ c« c« c« « z ss a a- a Sh a a ^33 M -S >» -o :c X •g.p i i c« -3 ® he 3 o V i- J£ X — ® "— a X '-3 ® '3 ^ £ ZD 3 5 3 ® ^ 3 .3 3: he — a a a a o ^ o "3: -§ 'be 3 £ o C X X Q X = E ? S' o a j-i « a J s « s O .E JO = 2 ^ a x: 3 ^ ^ ^ . I a "S: ' Sill ■„ Q D Q P X 3 ^ uj a 3 3 > o < t P 3 £ o .i: 0000 E E E E a a - ™ la xF 5 "qj S t 1 ^ ? £ ^ O ^ a. ^ V '73 a. , 3 -ti "« 3 o o o’ ® ^ o a 'a o ^ ^ 3 o CO 5 s 33 2 C 3 03 O 3 C V 3 a a >> -t-> .S »» • > > > > ala a a a a- ^ a; 1; 5 £ !&■, H E -® o p I o a* a c V ° lU =« 3 J u >> ® a -f 3 < 5 An interesting group which was not mentioned in the list given in the table because they are none too hardy in New England are the P.purpureo-maculatus varieties {P. Lemoinei X P. Coulter'i) ^ noted be- cause of the small spot of purple color at the base of each white flower petal. Shape Most everyone is familiar with the tall, upright, often arching habit of the old-fashioned P.coronarius. For many years, particularly prior to the introduction of the hybrids and some of the species, this was taken as being indicative of the entire group. Today, however, if shape were the only character in which we were interested, we could get a Philadelphus {P.coronarius nanus) which is a dwarf grow- ing, dense, compact, round-topped plant, seldom getting over \h feet tall ; or fairly low arching Philadelphus that look considerably like deutzias except that they are considerably more graceful as for exam- ple certain P. cymosus or P. Lemoinei varieties like P. Lemoinei “Ava- lanche” ; or still other round growing forms which face to the ground well like P.inodorus and P.splendens. This group contains some of the best Philadelphus for general land- scape use, simply because of their excellent, mound-like form. Their branches face to the ground well, making it possible to use them in the foreground or even as specimen plants where they may be ob- served all the time. Even when not in flower, their drooping branches and general rounded form is outstanding all the year and hence they can be well used where this characteristic is desired. Pruning and Use Mock-Oranges, as well as many of the honeysuckles and forsythias, need some renewal pruning every few years. The older branches might well be thinned out at certain intervals. This need not be done all at once unless necessary, but at least over a period of years. Thinning out, cutting back the old or dying branches to the ground, is much the best method to use on these plants as a group. Certain species may tend to get bare of branches at the base and when this occurs a careful cutting back is in order. All members of this genus can stand severe pruning, since they are all vigorous growers, and, if the occa- sion demands may be cut down to the ground entirely and will come up in a comparatively short time. Consequently then, though the Philadelphus are used primarily for their lovely flowers in June, there are certain types more fragrant than [60] The handsome Philadeiphus sp/endeits others; there are eertain types with larjjer Howers or more interesting riowers than others, and above all, there are different forms available, making them useful for different landscape purposes the entire year. Tall-growing species, like P. pubesceus^ might well be used in back- ground plantings for the foliage is comparatively free of insect and disease pests. Others, like P. splendens, P. Lemoiuei **Avalanche,“ etc., can be used as specimen plants. In hot, dry situations the P. coronarius type has been successfully used as a screen and even as a clipped hedge. A good, fast-growing, vigorous group of plants which can be used for various purposes and an excellent group on which to demonstrate that a few of the best well selected types will be per- fectly adequate to exemplify the many offered in the trade today. Victor Lemoine A general discussion of the Philadelphus group would not be complete without a word about Victor Lemoine, that great French nurseryman who has done so much to enrich our supply of ornamen- tal plants. Many of the varieties of Philadelphus, highly valued in the trade today, can be traced directly to the nurseries of Victor Le- moine and his successors. Born of a long line of horticulturists in 18"23, he graduated from college and learned his gardening practically, working for others until he was finally able to branch out for himself. Among the places at which he worked was that of Louis Van Houtte, at Ghent, Belgium. Lemoine established his business in 1850 at Nancy, France. Since that time the firm became one of the leaders in the world for hybrid- izing and introducing new varieties of woody plants. The number of different plants with which he worked is astounding. Some of them include Gladiolus, Paeonia, the double-flowered Begonia, Deutzia, Diervilla, Delphinium, Heuchrea, Syringa, Philadelphus and many others. During his life, he was the recipient of many outstanding horticultural honors, including the George Robert White Medal, pre- sented by the Massachusetts Horticultural Society in 1911. When he died in 1911, horticulture lost a man who did more than any one else in modern times in originating new varieties of ornamental woody plants. Donald Wyman [62] ARNOLD ARBORETUM HARVARD UNIVERSITY BULLETIN OF POPULAR INFORMATION Series 4. Vol. IV JULY ll, 1936 Number 11 SOME OF THE RARER SUMMER BLOOMING SHRUBS The Stewartias. At the Arboretum, the Stewartias started bloom- iiig at the end of June this year, though ordinarily they usually bloom a week or two later. They all have flaky, cinnamon-brown trunks, with white Camellia-like flowers. There are three types which can be considered here, namely Stewartia pentagijna, S. pseud oca mellia, and S. koreana. The first mentioned is the only one of the group native to this country, found from North Carolina to Florida. It is a shrub or tree-like bush with ovate to oblong-ovate leaves about *2-5 inches long. The cup-shaped flowers are white and about 3— inches across, while the beauty of the individual flowers is considerably augmented by the orange colored anthers. There is a variety, grandijiora , which is even more beautiful because of its purple stamens. This is appar- ently perfectly hardy at the Arboretum and another large plant on the campus at Vassar College at Poughkeepsie, N. Y., suffered no in- jury there at all during the severe winter several years ago. An added advantage of this plant is that the dark green leaves turn an orange to crimson color in the fall. The Japanese representative of this group is Sfeicartia pseudocamel- lia. In Japan, where this plant is (piite common around Nikkoand in other mountainous regions, Wilson found it rather rare in cultivation and difficult to purchase, for some reason or other. 'I'he young plant has ascending branches forming a vase-shaped crown, but older trees become rounded at the top. The flowers are borne singly in the axils of the leaves of the current year’s growth and there is a striking sim- ilarity between its flowers and those of a Camellia. In the fall, the leaves turn a blackish-purple color. i'he Korean Stewartia, S. koreana^ was first introduced in 1917 by [ ] JUL 131CC3 the Arboretum from seeds collected in Korea. 'I’he unfortunate thin*): about this plant was that it took eleven years before it bloomed, but it is probably the most hardy of the i^roup and certainly the most sym- metrical as a small tree. It is uiirij^ht and pyramidal in shape with the leaves a j^ood dark ‘jreen color. 'I'he edjres of the flower petals are slijjhtly frinjred and the stamens are a rich yellow. Albizzia julibrissin rosea. Commonly called the silk tree, this is the most outstandin*; of the summer bloominf): shrubs at the Arbore- tum and has the most finely divided foliaj^e of any of the woody plants hardy in the northern United States. I'he folia:■ 7 '^^ 7rV;iA.>?^ -' 5-'^,/ -7 7 ;; - 4^ i/ ' . ■> . V /? 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