1884.] The Exhalation of Ozone by Flowering Plants. 341 
In the case of the guaiacum test there are so many interfering 
conditions as to render it nearly valueless. Thus it will not only 
react in the presence of peroxide of hydrogen-and the oxides of 
nitrogen, but even the oxygen of the atmosphere is said to impart 
to it a tint hard to distinguish from the coloration due to ozone. 
The color scales were not used in these researches, as they are 
very difficult to obtain and, furthermore, the object here was not 
so much to ascertain the degree of coloring of the test papers as 
the single important fact whether plants have the power of gen- 
erating ozone. 
In noting the results obtained, the terms “ marked,” “slight” 
and “very slight” are used to express, in a general way, the ex- 
tent of blue coloration. This plan is deemed preferable for the 
reason that the tints, in most instances, were not very striking. 
My first observations were conducted in Horticultural Hall, 
Fairmount Park, Philadelphia. It was thought that a careful 
testing of the air of this hall, filled as it is witha profusion of 
plants, mostly of the foliage varieties, would give results suffi- 
ciently striking to be of value in clearing up the subject. In this, 
however, I was measurably disappointed, as will be seen hereafter. 
The hall has several compartments. The so-called main hall, of 
about the following dimensions: 220 feet in length, 100 feet in 
width and, the dome-like roof being of glass in the center, 65 
feet high. The room is filled with a variety of species of palms, 
bananas, monesteras, colocasias, caladiums, ferns, Ficus elastica, 
bamboo canes, Australian and New Zealand pines and numbers 
of smaller foliage plants. Average temperature of the hall 
during the time of experiments, 70° Fahr. 
On either side of the main hall are several smaller ones in 
_ Which the air was likewise tested, known under the names fern 
- forcing house, temperate house, propagating house and 
_ “sonomic house,- The. dimensions of these rooms are, length 100 
oes, width 30 feet, ceiling, curvilinear and of glass, 20 feet in 
_ “eight. The temperate house contained half hardy plants, as the 
, Ser. lemon, hibiscus, and a number of azalias in bloom. 
rcing house contained bedding plants, geranium, colius and — 
: yranthes, but few blooming, mostly cuttings. Economic 
© Contained pitcher plants, tea, coffee, chocolate, sugar, yapas, 
ua and aromatic plants. Propagating house is located out- 
The the main building, and contained geraniums in bloom. 
house was well stocked with ferns. 
