86 



THE CANADIAN HORTICULTURIST 



April, 1907 



very hardy everywhere. It grows to a 

 height of two feet. 



Virginia CowsUp, Mertensia Virginica, 

 is one of the best perennial plants in the 

 garden. It is like the corydalis, dis- 

 appearing soon after blooming. Such 



plants should be kept staked to mark 

 the place where they will appear the 

 following season. This plant grows 

 two feet high, producing beautiful sky- 

 blue flowers that are always admired by 

 everv' passer-by. 



Leopard's Bane, Doronicium excelsum, 

 grows to a height of two feet and pro- 

 duces yellow, sunflower-like blooms on 

 long stems which are very good for cut- 

 ting. It is a very free-blooming plant 

 and makes a grand display in the border. 



SKade Trees for Our Cities^ 



Prof. D. P. Penhallo-w, McGill University, Montreal 



THE question of shade trees for our 

 cities and towns, is a many-sided 

 one, which has engaged the most 

 careful consideration from a very early 

 period in our history. Shade trees, as 

 well as properly kept shrubs and flower 

 beds, exert a powerful reflex influence 

 upon those who are habitually asso- 

 ciated with them in their daily lives. 

 From this point of view it is therefore 

 not difficult to determine that the ex- 

 tent to which trees are cultivated, and 

 the intelligence expended in properly 

 caring for them, may be safely adopted 

 as an index of the relative progressive- 

 ness, culture and civiUzation of a town. 

 In discussing the relation of shade 

 trees to purposes of street ornamenta- 

 tion, there are three factors of leading 

 importance which should be taken into 

 consideration: Their productive value; 

 their esthetic value; and their educa- 

 tional value. The popular notion that 

 trees have a tendency to reduce the 

 actual temperature of the surrounding 

 air, has a slight basis of fact in a dense 

 forest, but in the case of individual 

 trees, their influence in this respect is 

 so small as to ibe wholly unrecogniz- 

 able; nor is it more conceivable that 

 the thousands of trees which might be 

 scattered throughout a large city, would 

 exercise any more appreciable effect. 

 Having thus eliminated what at first 

 sight might reasonably be expected 

 from the growth of trees, it is pertin- 

 ent to ask in what respects they are 

 protective? Trees constitute an ac- 

 tive medium for the transfer of water 

 from the soil to the atmosphere through 

 their foliage, and the amount of water 

 which may be translocated in this way, 

 is very large during the period of ac- 

 tive growth. There is therefore a con- 

 stant tendency to maintain the atmos- 

 phere in a condition of desirable hu- 

 midity, and though this effect is rapidly 

 offset by the distributing influence of 

 air currents, it is nevertheless sensible, 

 and in this respect the presence of 

 large masses of foliage is a desirable 

 factor which tends to the amelioration 

 of otherwise severe conditions. 



Active foliage demands large sup- 

 plies of carbon-dioxide gas which it 

 draws from the surrounding air and 

 rapidly converts into organic bodies, 



♦Extracts from an article published in the Canadian 

 Municipal Journal. 



these latter being subsequently util- 

 ized in building up the fabric of the 

 plant body. In return, the plant yields 

 up a corresponding volume of free 

 oxygen, and the surrounding air is 

 purified to that extent. In large cities, 

 especially where there are extensive 

 manufacturing interests as in Mon- 

 treal, there is a tendency towards the 

 local accumulation of the noxious pro- 

 ducts of combustion of which carbon- 

 dioxide is the most important, and 

 there can be no doubt that the pres- 

 ence of trees in large numbers exerts 

 a most salutary effect by virtue of 

 their absorption of this gas and the 

 substitution of pure oxygen. It may 

 reasonably be contended from these 

 statements, that a city which is abund- 

 antly suppHed with shade trees will, 

 in general, be distinguished by the 

 greater purity and more bracing qual- 

 ity of its atmosphere, and it would 

 seem to me that the relations thus de- 

 veloped, are too often overlooked or 

 even ignored in considering the part 

 which trees play in urban Hfe. 



There is another respect in which 



trees manifest their protective influ- 

 ence, as found in the extent to which 

 they minimize the effects of excessive 

 heat. Any one passing from a narrow 

 and crowded business street devoid of 

 trees, to a residential street provided 

 with shade trees, becomes sensible of 

 a gratifying difference in temperature. 

 This difference is not altogether de- 

 pendent upon the relative height and 

 the crowded character of the build- 

 ings, though it is a large factor; but it 

 is due, in the main, to the influence 

 of the trees themselves. The trees not 

 only give the pedestrian direct protec- 

 tion from the rays of the sun, but 

 they so shield the pavements and 

 buildings as to prevent the absorption 

 and reflection of heat, affording to the 

 buildings in particular, such a degree 

 of protection as to give to the inhabi- 

 tants a sense of refreshing comfort. 



Of the esthetic and educational value 

 of trees, much might be said, but it 

 may be sufficient to point out that to 

 bring up children habituated to asso- 

 ciation with those forms of vegetation 

 which typify great beautv and grace 



Shade Trees Such as These Increase the Value of the Residences 



