252 



HORTICULTURE 



.March 15, 1919 



ARNOLD ARBORETUM BULLETIN. 



Dwarf Conifers. Of many of the 

 cone-bearing trees there are abnormal 

 dwarf forms, and a few conifers are 

 naturally dwarf shrubs. The former 

 are of different origin; most of them 

 are seedlings, some have grown from 

 buds on branches of large trees, and 

 others have been produced by exposure 

 to excessive cold and high winds, and 

 these when transferred to more favor- 

 able surroundings often lose their 

 dwarf habit. A good example of a 

 dwarf of the last class is the depauper- 

 ate Larch which grows at the timber 

 line on Mt. Fugi in Japan. Seedlings 

 of this little plant raised in the Ar- 

 boretum twenty-five years ago are now 

 nearly of the same size as the seed- 

 lings of the trees of the Japanese 

 valleys raised at the same time. In 

 the sandy swamps of Prince Edward 

 Island Black Spruces not more than 

 two feet high produce cones and fer- 

 tile seeds, and near the timber line of 

 the White Mountains it is possible to 

 walk on dwarf mats of the Balsam Fir 

 which lower down on these mountains 

 is a tall tree. Transferred to better 

 soil where the winter climate is iess 

 severe these alpine and boreal dwarfs 

 would soon assume the tree habit of 

 the species. Dwarfs of some species, 

 however, which evidently owe their 

 habit to environment, retain the dwarf 

 habit when transferred to more favor- 

 able surroundings. Such dwarfs are 

 some of the forms of the European 

 Pinus montana from high altitudes 

 and some dwarf forms of Junipers 

 which reproduce the dwarf form in 

 their seedlings. Seedling dwarfs have 

 been produced by many different 

 species, but they are naturally most 

 numerous in species which have been 

 largely raised in nurseries where seed- 

 lings are carefully watched and ab- 

 normal forms are preserved. It is not 

 surprising, therefore, that trees like 

 the eastern Arbor Vitae and the Nor- 

 way Spruce have produced many such 

 forms in nurseries as few other cone- 

 liearing trees have been so largely 

 raised from seed. 



It is only In recent years that dwarf 

 conifers have attracted much atten- 

 tion, for Loudon in his "Arboretum 

 et Fruticetum Botanicum," published 

 in 1838 enumerates only ten. These 

 are two dwarf forms of Pinus montana, 

 two forms of the Norway Spruce, a 

 dwarf Cedar of Lebanon, a dwarf Red 

 Cedar (Juniperus rirginiana), a pros- 

 trate form of Juniperus sabina, and 

 two dwarf forms of Juniperus com- 

 munis. He knew no dwarf Arbor 

 Vitae, Chamaecyparis, Hemlock, or 

 dwarf form of Abies. Beissner in the 

 second edition of his "Handbuch der 

 Nadelholzkunde," published in 1899. 



enumerates one hundred and four 

 dwarf conifers in thirty-one species; 

 of these twenty-five are forms of the 

 Norway Spruce, eight are forms of 

 Lawson's Cypress {Chamaecyparis 

 Cawsoniana) , and eight are forms of 

 the Arbor Vitae of the eastern United 

 States. In addition to the plants 

 enumerated by Beissner there are a 

 few which originated in this country 

 and which do not appear to have been 

 known to him. 



There is a good but by no means a 

 complete collection of dwarf conifers 

 in the Arboretum, for it is difficult to 

 keep track of the new forms which ap- 

 pear in the nurseries where large 

 numbers of conifers are raised from 

 seed and are often given names with- 

 out descriptions, and some dwarfs like 

 those of Lawson's Cypress and the 

 Chinese Arbor Vitae are not hardy 

 here. The Arboretum collection Is 

 much visited, however, by nurserymen 

 for there is now a demand for these 

 plants, which have their uses in small 

 gardens and are less happily planted 

 in making low banks of foliage about 

 the base of suburban cottages. 



Perhaps the handsomest of the 

 dwarf conifers in the Arboretum col- 

 lection is a form of the Japanese Pinus 

 densiflora (var. umbraeulifera) . This 

 is a wide, vase-shaped plant which in 

 Japanese gardens is often ten feet 

 high and broader than high. The 

 leaves are of a bright cheerful green 

 and comparatively small plants flower 

 and produce minute cones. Among 

 the fourteen or fifteen dwarf forms 

 of the Norway Spruce none is hand- 

 somer than one of the varieties de- 

 scribed by Louden in 1839 (var. 

 I'lunbrasiliana). This is a low, very 

 compact, round-topped bush which 

 rarely grows more than three feet 

 high but spreads to a diameter much 

 greater than its height. The plant li 

 said to have originated on the Molra 

 estate near Belfast, Ireland, toward 

 the end of the eighteenth century and 

 to have been carried to England by 

 Lord Clanbrasil for whom it was 

 named. Equally good is the variety 

 nana which has a flatter top and does 

 not grow as tall as the Clanbrasiliana 

 but spreads into a broad bush. The 

 subglobose var. Gregoriana and the 

 variety prostrata are interesting 

 plants. Some of the dwarf Norway 

 Spruces, especially the variety Ellwan- 

 gcriana, have a tendency at the end 

 of a few years to form a vigorous 

 leading shoot and eventually to be- 

 come arborescent. 



Two dwarfs originated in the Ar- 

 boretum in 1874 among seedlings of 

 Pieea pungens, the Colorado Blue 

 Spruce and Abies lasiocarpa. The 

 original plant of the former is now 



seven feet high and ten or twelve feet 

 in diameter, and has so far escaped 

 the loss of branches which disfigures 

 this Spruce after it is thirty years old. 

 Although well worth the attention of 

 lovers of dwarf conifers, Pinus pun- 

 gens compacta is little known beyond 

 the limits of the Arboretum. The seed- 

 ling of Abies lasiocarpa retained its 

 dwarf habit for many years but h&! 

 now begun to grow more vigorously 

 and to assume the typical habit of the 

 species. The dwarf of the European 

 Silver Fir (Abies Picea compacta) be- 

 haves here in the same way and after 

 a few years grows out of Its dwarf 

 habit. There is in the collection a 

 small plant of a dwarf of Abies con- 

 color which is very compact, but It 

 is too soon to speak of Its value. The 

 well known dwarf of the Balsam Fir 

 (Abies balsamea var. hudsonica) la a 

 real dwarf only a few inches high. A 

 number of seedling forms of the White 

 Pine (Pinus Rtrobus) and of the 

 Scotch Pine (Pinus sylvestris) are in 

 the collection, but the best known and 

 most generally planted dwarf Pines 

 are the mountain forms of the Euro- 

 pean Pinus montana which appear In 

 the catalogues of nurserymen as Pinut 

 pumilio and P. Mughus. There are 

 many forms of this hardy dwarf; they 

 are broad shrubs with erect or semi- 

 prostrate stems and are rarely more 

 than ten feet high, but often much 

 broader than tall. Seedlings of these 

 plants show great variation in size and 

 habit, and new forms are constantly 

 found in nursery seed-beds. The 

 dwarf form of the Douglas Spruce 

 (Pseudotsuga Douglasii var. globosa) 

 has proved one of the slowest growing 

 of these plants in the Arboretum col- 

 lection. 



In the common Hemlock of eastern 

 North America the tendency to varia- 

 tion in seedling plants is unusually 

 strong and dwarfs differing in size, 

 shape and vigor are often found in 

 the neighborhood of Hemlock groves. 

 Some of these have been propagated 

 and have received names but as differ- 

 ent names have been used for the 

 same or nearly the same forms it is 

 not now possible, even if it were de- 

 sirable, to distinguish all these dwarf 

 Hemlocks by name. 



Among the seedlings of the Arbor 

 Vitae of eastern North America are 

 found some of the handsomest of the 

 dwarf conifers. There is a large col- 

 lection of abnormal forms of this tree 

 in the Arboretum collection and 

 among them none are better than 

 those called "Little Gem," compacta 

 and Hoveyi. Seedlings of the Jap- 

 anese Retinosporas (Chamaecyparis 

 obtusa and pisifera) show, too, a great 

 tendency to variation. One of the 



