BOTANY. 291 



posure of their under surfaces to light, the increase being double, 

 triple, or even more. It is obvious, that this is one principal cause of 

 the unhealthiness of leaves, which results from the inverted position 

 being forced upon them. -Another cause is to be found in the diminu- 

 tion of the rate of decomposition of carbonic acid, which takes place 

 under the same circumstances, and to about the same extent. Accord- 

 ing to Prof. M., the exhalation is greater under blue glass than it 

 is in diffused light, and the difference in the amount of it from the 

 upper and under surfaces respectively is most strongly marked ; on 

 the other hand, the amount of exhalation under red glass is reduced 

 to about a sixth, and the difference between the quantity exhaled from 

 the two surfaces is proportionably lessened 



THE POLAR PLANT. 



AT the last meeting of the American Association, a communication 

 on the polar plant was presented from Major Alvord, U. S. A. 

 This plant, which is also known as the compass plant, derives its 

 name from the fact, that its lower leaves are said to present their 

 faces uniformly to the east and west, the plane of the leaf being 

 north and south, or coinciding with the meridian plane, ft is found 

 abundantly in various portions of the West, particularly in the vicinity 

 of Fort Leavenworth, in Southern Michigan, and on the prairies 

 generally from Texas to Iowa. In the valleys, or lower portions of 

 the rolling prairies, w r here most sheltered from the winds, the polarity 

 of the leaves is most accurate, and the plants are seen arranged all 

 parallel to each other. This is true of the radical leaf, from one to two 

 feet in height, before it grows up to the flowering plant, as it does in 

 the second year. The peculiarities of the plant are well known 

 and recognized by the hunters, trappers, officers of the army, and 

 others, who have traversed the prairies, and it is said that the Indians 

 are accustomed to make use of it as a guide in cloudy weather. As 

 the polarity of the plant has been called in question by some dis- 

 tinguished botanists, Major Alvord referred to the statements of nu- 

 merous distinguished officers, none of whom, in any of their prairie 

 expeditions, have ever noticed a departure of the leaves from their di- 

 rection, except when there was some assignable cause apparent to in- 

 terfere with its growth, such as winds, the trampling of buffalo, or cat- 

 tle, &c. In endeavoring to account for this seeming polarity, some 

 have suspected the presence of iron, in some of its compounds, in the 

 plant, but a careful analysis with the most delicate tests gave no trace 

 of it. Others have conjectured that the polarity is due to electrical 

 currents, as the plant is full of resinous matter, and is sometimes called 

 the rosin-weed. 



A note from a gentleman in Wisconsin was then presented by Dr. 

 Gray, which describes the plant as follows: "The large radical 

 leaves of this species of the sun-flower tribe, when growing in tufts 

 or bunches on the dry, open prairies, rise so much above the grassy 

 turf as to form conspicuous objects ; and when thus exposed, they 

 generally present their flat surfaces towards the rising and setting sun, 



