THIs long agitated question is now definitely set at rest by the experiments of Prof. It. C. Kedsie, of the Michigan Agricultural College, and are thus related in a letter of his to Governor Holt:

Not to leave this matter in the condition of mere conjecture, I have gathered and analyzed specimens of air from a room where the influence of growing plants would be exhibited in a greatly exaggerated form. Thus, instead of taking the air from a room containing a few plants, I 'gathered it from the college greenhouse, where more than 6,000 plants are growing. I gathered the air before sunrise on the mornings of April 16th and 17th; the room had been closed for more than twelve hours, and if the plants exhaled carbonic acid to an injurious extent, the analysis of air from such a room would certainly disclose this fact. The three specimens of air gathered on the morning of April 16th from different parts of the room, gave 4.11, 4.00 parts of carbonic acid in 10,000 of air, or an average of 4.03 in 10,000. The two specimens of air gathered April 17th, gave 3.80 and 3.80 parts of carbonic acid in 10,000, or an average on the whole of 3.94 parts of carbonic acid in 10,000 of air, while the out-door air contains 4 parts in 10,000. It will thus be seen that the air in the greenhouse was better than "pure country air." This deficiency of carbonic acid was doubtless due to the absorption of carbonic acid and consequent accumulation of oxygen during daylight, since the windows of the greenhouse were closed day and night on account of the cool weather.

To ascertain whether the air of the greenhouse had more carbonic acid by night than by day, I gathered two specimens of air in different parts of the house, at 2 o'clock P. M., April 17th. These gave 1.40 and 1.38 parts of carbonic acid in 10,000, or an average of 1.39 parts, showing that the night air contained more carbonic acid than did the air of day.

Now, if a room in which were more than 6,000 plants, while containing more carbonic acid by night than by day, contains less carbonic acid than any sleeping-room on the continent, we may safely conclude that one or two dozen plants in a room will not exhale enough carbonic acid by night to injure the sleepers.

It is so easy, to be deceived by a name! I. lately saw an article showing the beneficial and curative influence of flowers in the sick room. Instances were related where persons were cured by the sight and smell of flowers, and withcut question their influence is good. Yet flowers exhale this same carbonic acid by day and by night! The flowers, by their agreeable odor and delicate perfume, impart an air of cheerfulness to the sick chamber which will assist in the recovery from lingering disease, notwithstanding the small amount of carbonic acid which they constantly exhale.

The presence or absence of carbonic acid is not the only question in regard to the healthfulness of plants in a room. The state of moisture in the air of the room may become an important question, especially in the case of persons afflicted with rheumatic or pulmonary complaints. But I will not take up that subject.