446 POPULAR SCIENCE MONTHLY. 



gases, products of putrefaction, so actively poisonous to man, are 

 absorbed, and in the process of vegetable digestion the deleterious 

 portion is separated and appropriated by the plant, while oxygen, 

 the element essential to animal life, is returned to the air. Trees, 

 therefore, in cities, are of immense value, owing to their power to 

 destroy or neutralize malaria, and to absorb the poisonous elements 

 of gaseous compounds, while they render the air more respirable by 

 emitting oxygen. 



The conclusion from the foregoing facts is inevitable that one of 

 the great and pressing sanitary wants of New York city is an ample 

 supply of trees. It is, in effect, destitute of trees; for the unsightly 

 shrubs which are planted by citizens are, in no proper sense, adequate 

 to the purpose which we contemplate. Its long avenues, running 

 north and south, without a shade tree, and exposed to the full effect 

 of the sun, are all but impassable at noonday in the summer months. 

 The pedestrian who ventures out at such an hour finds no protection 

 from an umbrella, on account of the radiation of the intense heat 

 from the paved surface. Animals and man alike suffer from ex- 

 posure in the glowing heat. Nothing mitigates its intensity but 

 the winds or an occasional rainstorm. And when evening comes on, 

 the cooling of the atmosphere produced by vegetation does not occur, 

 and unless partially relieved by favoring winds or a shower the 

 heat continues, but little abated, and the atmosphere remains charged 

 with noxious and irrespirable gases. It is evident that shade trees, 

 of proper kinds, and suitably arranged, supply the conditions neces- 

 sary to counteract the evils of excessive heat. They protect the 

 paved streets and the buildings largely from the direct rays of the 

 sun; they cool the lower stratum of air by evaporation from their 

 immense surfaces of leaves; they absorb at once the malarious 

 emanations and gases of decomposition, and abstract their poisonous 

 properties for their own consumption; they withdraw from the air 

 the carbonic acid thrown off from the animal system as a poison, and 

 decomposing it, appropriate the element dangerous to man, and give 

 back to the atmosphere the element essential to his health and even 

 life.* 



And we may add that cultivated shade trees in New York would 

 be an artistic and attractive feature of the streets. Every citizen 

 enjoys trees, as is evident from the efforts made to cultivate them 

 throughout the city. 



It is frequently alleged that trees can not be successfully culti- 

 vated in cities on account of the gases in the soil. There are ample 

 proofs to the contrary. The city of Paris strikingly illustrates the 



* The late Dr. Francis remarked that he had noticed a marked increase in the fatality 

 of diseases in sections of the city after the removal of trees and all vegetation. 



