BOTANICAL GAZETTE. 8i 



We make no apology for making some extracts from a paper which 

 deals with a subject of universal interest : 



"The old question of the effects of living plants on the air of 

 houses is one of considerable interest. The family doctor is often 

 confronted with the query, "How do plants in rooms affect the health 

 of the inmates ? " Formerly, it was the universal opinion that they 

 were injurious to health, particularly in the sleeping room and sick- 

 chamber. Unfortunately, this still continues to be a popular impres- 

 sion. To review the various views on this topic, down to the present, 

 would be foreign to the scope of this article and quite out of place. 

 The discussion will necessarily be confined to the present state of our 

 knowledge concerning this subject, and especially such of its bearings 

 as are interesting from a medical point of view. 



"Three of the chief functions in plant life are the absorption of 

 carbonic acid, the exhalation of oxygen, the generation of ozone. 

 Now, it has been conclusively shown that variations in the amount of 

 these gases from the presence of any number of plants h^^^'e no ap- 

 preciable effect on the air of an apartment, the absorption and exhala- 

 tion of these substances being carried on too slowly either to improve 

 or to vitiate the air. 



There is, however, yet another process in plants, which in this 

 connection is of far greater importance, viz., that of trafispiration. By 

 this term is meant the exhalation of moisture by the leaves. About 

 this function very little was known until recently. Careful investiga- 

 tions of the subject have been made by the writer to which brief ref- 

 erence only can be made here, for ihey have formed the basis of a 

 paper elsewhere It may suffice t"; say that the average rate of trans- 

 l)iration for plants having soft, thin leaves, as the geranium, lantana, 

 etc., is one and half ounces (by weiglit) of watery vapor per square 

 foot of leaf surface for twelve diurnal h^urs of clear weather. In or- 

 der to convey some notion of the great activity of this function, it 

 might be stated that at the above rate the Washington elm, at Cam- 

 bridge, Massachusetts, with its two hundred thousand square feet of 

 leaf surface, would give off seven and three quarter tons of water in 

 twelve hours. In the twenty-four hours an in door plant will tran- 

 spire more than half as much as one in the open air. It would ap- 

 pear to follow naturally from these fa' ts that growing plants would be 

 capable of raising the proportion of aqueous vapor of the air of 

 closed apartments. And this suggestion prompted the writer to make 

 observations with the view of establishing this fact experimentally. 

 By means of the hydrometer, the atmosphere of 

 two rooms at the Episcopal Hospital, in which the 

 conditions and dimensions were m every respect similar, 

 were tested simultaneously, in order to note the variations produced 

 by growing plants. In the vvindow of one of the rooms vvere situated 

 five thrifty plants, the other contained none. 



For eighteen consecutive days the dew-point of the room con- 

 taining plants gave an average complement one and a half degrees 

 lower than the room in which there were no plants. Thinking that 



