Page:Popular Science Monthly Volume 46.djvu/516

 introducing variations of one at a time. Then, whatever differences are observed in the results obtained at the end of a certain time, are evidently due to the factor which has been changed. In studying the modifications caused by the hygrometric conditions of the air, M. Lothelier capped two specimens of barberry with a long cylinder of glass, along which he placed broad-mouthed flasks of sulphuric acid to absorb the moisture of the air; and two other plants with a similar tube along which were flasks filled with water. These two lots of plants, growing side by side under

 —1 and 2, Berberis (barberry grown under moist and under dry conditions); 3 and 4, Genista or broom, moist and dry; 5 and 6, Ulex, or furze, moist and dry; 7 and 8, Cirsium, moist and dry; 9 and 10, Pyracantha, moist and dry; 11, Xanthium, upper sprig moist, lower sprig dry; 12 and 13, Gleditscha, or honey locust, grown in the sun and in the shade; 14 and 15, Robinia, or locust, grown in the sun and in the shade; 16 and 17, Rosa, grown in the sun and in the shade.

the same conditions of light, temperature, and watering, were then experimented upon for about six weeks, at the end of which it was found that the new leaves of the plants in dry air were spiny, while the leaves of the two in moist air were well developed, and had acquired long petioles. Like experiments were instituted on other plants, with always the same results; the differences of appearance presented by these plants as they grew in dry or moist air were really remarkable, and so great as almost to suggest that they were of different species.

An interesting observation was made that the disappearance