500 



THE POPULAR SCIENCE MONTHLY. 



introducing variations of one at a time. Then, whatever differ- 

 ences 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 



Plants -wiTn Thorns. 1 and 2, Berleris (barberry grown nnder moist and under dry con- 

 ditions) ; 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, Fi/racantha, moist and dry ; 11, Xan- 

 t/iium, upper sprig moist, lower sprig dry ; 12 and 13, GlediischiK, or honey locust, 

 grown in the sun and in tlie shade ; 14 and 15, Rohinin., or locust, grown in the sun and 

 in the shade ; 16 and 17, lioia, 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 devel- 

 oped, and had acquired long petioles. Like experiments were 

 instituted on other plants, with always the same results ; the dif- 

 ferences 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 



