July 6, 1892.] 



Garden and Forest. 



323 



trees and shrubs to so change their shapes is the wind. When 

 we see such trees and shrul)s painted on a canvas we know at 

 once that tiic landscape is a wind-beaten one, and that the 

 vegetation is struggling against a force which is trying to de- 

 stroy its foothold. 



"But while the wind is especially active on the sea-shore in 

 clianging the natural, or perhaps the original form of the trees 

 and shrubs, it is similarly effective to a lesser degree in any lo- 

 cality at all exposed to winds. The interior plains, the cliffs on 

 tlie sides of the desert, the high mountain-peaks, the elevated 

 plateaus, the table-mountains, the slopes of the more sheltered 

 sides of islands — in fact, everywhere — may the power of the 

 wind be perceived. 



"The effects of the wind may be temporary or permanent ; 

 temporary, if the plant retains its original form and outward 

 appearance when removed from the windy region to a shel- 

 tered one. This is by far the most common elTect, and espe- 

 cially refers to shrubs. I\Iany instances may be cited, but I 

 will only mention one. Baccharis pilularis, which grows 

 everywhere on the coast around San Francisco, clings typically 

 to the soil and sand-hills where exposed to the wind, while on 

 the north side of Tamalpais, where the shelter is perfect, and 

 even in the Oak-scrub of Golden Gate Park, it assumes an erect 

 form. So different is the outward appearance between these 

 two forms that the former has been described as a distinct 

 species, B. consanguinea. 



"Similarly on nearly all our high mountain-tops we meet 

 with Scrub Pines growing in the crevices and clinging to the 

 rocks like real coverlets of verdure. But the same species 

 may be found farther down in the elevated valleys growing 

 erect with sloping branches and undivided trunks. Such in- 

 stances are common. I may, however, here especially recall 

 the dwarf and scrubby Pinus monticola, growing in the canons 

 on the slope of Mount Dana, while farther down splendid 

 specimens are crowding the sheltered meadows. 



" As an instance, again, where the effects of the wind have 

 been partly permanent we may point to the IVIonterey Pine (P. 

 insignis) and to the Monterey Cypress (Cupressusmacrocarpa). 

 Mature specimens of these varieties assume always horizontal 

 crowns, even when growing inland, and only during their 

 earlier growth do they show a tendency to grow erect like most 

 species of Pines or coniferous trees generally. We may pre- 

 sume that if the evolution of a species is accompanied by this 

 continued wind force tlie latter will, to a great degree, mould 

 the outward form of the species. If, again, the evolution of a 

 species takes place under various conditions of wind and calm 

 the form of the species will be variable, according to exposure. 



"Tlie effect of the wind, while apparent everywhere, and 

 while found in every climate and in every country, is, how- 

 ever, not the most powerful agent in shaping the forms of 

 trees and shrubs. The snow which part of the year covers 

 vast territories, often to a depth of thirty or more feet, has a 

 great influence upon the forms of all plants which are exposed 

 to it for a longer or shorter time. 



" As the effects of the snow depend chiefly upon the resist- 

 ance to pressure, it will be seen that evergreen and deciduous 

 trees must be unequally affected. The foliage of the ever- 

 greens offers much more resistance to the snow than do the 

 bare hmbs of trees and shrubs which during the winter season 

 are void of leaves. In some horticultural districts, where snow 

 but seldom falls, and where, accordingly, such trees as Olives, 

 Oranges and Lemons are cultivated successfully, an occasional 

 fall of snow may do, and has in many instances done, consid- 

 erable harm. We know that when the snow lodges on the 

 evergreen and upright limbs of Orange-trees, these limbs be- 

 come so heavy that they break down, more or less ruining the 

 trees." ..." Those limbs which point upward do not yield 

 readily under the pressure of the snow, and trunks which are 

 repeatedly forked will, if the pressure is heavy enough, split 

 lengthwise. In case the trees in question had possessed down- 

 ward sloping limbs and an upright, undivided or standard 

 trimk, the effect of the snow pressure would have been less 

 dangerous ; the limbs would have yielded to their snow bur- 

 den, which, when melting, would have slipped off, leaving the 

 limbs free, and the undivided trunlvs would not have split, and 

 the trees would have escaped without injury. If such snow- 

 falls were frequent and regular, only such varieties could be 

 cultivated as were possessed of downward sloping limbs and 

 upright trunks. All trees shaped otherwise would gradually be 

 ruined and their cultivation become impossible. These last 

 remarks refer only, or at least principally, to evergreen trees. 

 If the Orange-trees, which we gave as an example, instead of 

 being evergreens were deciduous — that is, presenting only 

 bare limbs in the winter, like Peaches, Apricots and Pears — 

 the pressure of the snow would not have injured them, at 



least not by breaking their limbs and splitting their trunks, and 

 their cultivation would not necessarily have been abandoned. 

 If we consider a forest instead of a horticultural district, we 

 will iind that the conditions are there very much the same. 

 The yearly snowfall, if only heavy enough, tends to break 

 down and destroy all wild evergreen trees which do not pos- 

 sess a form suitable to resist the heavy snow mantle. Trees 

 which would thus sul'fer would be all evergreen trees, with 

 spreading crowns, such as Live Oaks, Laurels, Madrofia, cer- 

 tain Pines, such as Monterey Pine, Digger Pine (Pinus Sabini- 

 ana), Italian Pine (P. Pinaster), Lebanon Cedar, and the hun- 

 dreds, if not thousands, of other evergreen trees which inhabit 

 regions below the regular snow-line. 



" Nature thus eliminates from snow-visited forests all ever- 

 green trees which are not suited to resist the pressure of the 

 snow. On the contrary, the snowfall makes it possible for all 

 those trees to live and survive which, through their outward 

 form, are able to easily shed the accumulated snow. As re- 

 gards deciduous trees, no such upright trunks and sloping 

 branches are necessary, as the bare limlis do not accumulate 

 the snow or suffer under pressure. If the above is true, the 

 forests of snow-visited districts will be found to consist of oijly 

 such varieties of trees as possess the requisite form — that is, 

 evergreen trees with upright, undivided trunks and downward 

 sloping branches, as well as of deciduous trees of various not 

 especially characteristic forms. Upon examination this will 

 also be found to be the case. 



" A visit to the high Pine-forests of Sierra Nevada shows us 

 just such forests. Nowhere is the snowfall heavier and no- 

 where is the characteristic form of the evergreen trees more 

 pronounced. This is also the case in all other snow-visited 

 regions where forests are at all able to exist. Where the snow- 

 fall is the heaviest and lasts the longest all evergreen trees, at 

 least during a certain period of their life, possess the required 

 pyramidal form. Evergreen trees of any other form would in 

 their struggle for existence have little or no chance to com- 

 pete with better-equipped neighbors. It follows, also, that the 

 less the snowfall the less characteristic will prove the pyra- 

 midal form in all evergreen species, while lower down the 

 mountains on the warmer slopes the pyramidal form may be 

 expected to be entirely absent. 



"To refer to our nearest high mountains, the Sierra Nevada, 

 we find thus on the snow- belt such trees as Pseudotsuga taxifolia, 

 Abies aniabilis, Pinus Lambertiana, Libocedrus decurrens. Se- 

 quoia gigantea, etc. All these show in a characteris^tic way the 

 pyramidal form, the snow-shedding branches and the undi- 

 vided trunk. We find in this region no large Live Oaks, nor 

 any large evergreen trees of globular or goblet shape. But in 

 the region immediately below the heavy snow-belt the charac- 

 teristic pyramidal shape is entirely absent. The forms of the 

 evergreen trees are here evidently regulated by other agencies. 

 In this region we meet with several evergreen Oaks with large 

 crowns, spreading branches and repeatedly divided trunks. 

 The Pines also, like P. Sabiniana, are characterized by their 

 forked trunks, their upright limbs, and by their general resem- 

 blance to deciduous trees. As regards shrubs of all kinds, 

 they are hardly less influenced by snowfall. In the snow-vis- 

 ited forests, at least, the evergreen shrubs show a low de- 

 pressed form, sometimes spreading out like dishes on the 

 ground. Other species, again, like the Manzanitas, possess 

 repeatedly zigzag bent limbs especially adapted to resist the 

 pressure of snow and wind. Such zigzag form is also pos- 

 sessed by the branches of trees, greatly assisting tliem to re- 

 sist outside pressure of any kind. Thus, while the lower or 

 central branches of most of the Pines in the snow region slope 

 downward, the upper limbs, which are naturally less exposed 

 to snow pressure, assume a horizontal position, but are com- 

 pensated by being repeatedly bent and furnished with heavy 

 knees. Such limbs are generally seen in the various species 

 of Pines, such as P. Lambertiana, P. contorta, P. Jeffreyi ; also 

 in Sequoia gigantea, etc., while they are almost absent in the 

 Spruces and Firs, the sloping elastic limbs of which continue 

 to the tops." 



Notes. 



The Clarke Memorial Medal was recently bestowed by the 

 Royal Society of New South Wales upon Mr. Thistleton Dyer, 

 director of the Kew Gardens, in recognition especially of the 

 valuable services which he has rendered to the agricultural 

 and horticultural interests of India and the Colonies. 



The Japanese Ligustruin Ibota is still too rarely seen in our 

 gardens. It is one of the very hardiest and most desirable of 

 the shrubs of its class, and just now it is covered with its short 

 drooping racemes of pure white flowers which are so fragrant 



