1876.] Hygiene of House Plants. 671 
find great relief as they enter a greenhouse and breathe its air; 
even those whose complaint prevents comfortable rest elsewhere 
find little or no trouble in sleeping in a greenhouse. Thus all 
the facts at our command tend to prove that the air of green- 
houses, despite its exceeding dampness, is not unhealthy, but 
rather the reverse. Luxuriant vegetation growing in very moist 
air is not necessarily so unwholesome as is usually supposed. 
Mr. Bates, in The Naturalist on the Amazon, speaks of certain 
localities in which he spent some time, where the air was as if 
filled with steam at times, and always very full of aqueous vapor, 
and where the vegetation was wonderfully rank; and yet he 
found these places unusually healthy, free from many complaints 
common in drier regions near by. This is perhaps an exception, 
rather than an example illustrating a general rule, but it is worth 
some notice. 
If house plants are to thrive, they must have abundance of 
fresh air and sunshine. And now that fine window plants are so 
generally desired, there is doubtless often a severe struggle in the 
mind of many a housekeeper, to decide whether the plants shall 
suffer and perhaps die, or upholstery and carpets be allowed to 
fade. The plants seem usually victorious, the windows are 
Opened for more pure air, the shutters for more light, and the 
home becomes more cheery, attractive, and healthful. The air 
heated by stove, furnace, or worse, by steam-pipes, is almost 
sure to be very dry, so much so as to be irritating and hurtful to 
the Tespiratory organs. As has been noticed, the leaves of plants 
exhale moisture, often to a considerable amount, and a dry air, 
if brought into contact with growing plants, is furnished with 
Some of the lacking aqueous vapor. This process 18, to a certain 
extent, self-regulating, for the drier the air the more rapid is the 
exhalation from the leaves, while this decreases as the moisture 
of the air increases. Another effect which might have considera- 
‘ > influence upon greenhouse air, but would not amount to much 
_ M occupied rooms, where but few plants are kept, is their tend- 
_ “Y to equalize the temperature. In most cases plants do not 
Nse in temperature as quickly as does the air about them, and 
While the air grows warmer during the day, and is at T T 
_ Mum seyeral hours before sunset, plants go on increasing in tem- 
_ Perature for some hours after the air has begun to grow cooler, 
and thus as the air cools the radiation from plants warms it, while 
_ firing the day the exhalation of moisture tends to cool the air. 
: far we have considered vegetation only in its ordinary 
