HABITS OF CLIMBING PLANTS. 161 



teenth revolution the internode had grown from 1| to 6 inches 

 in length, and carried an internode 1| inch long, which was 

 just perceptibly moving ; and this carried a very minute ulti- 

 mate internode. After the 21st revolution the penultimate 

 internode was 2| inches long, and probably revolved in a 

 period of about three hours. At the 27th revolution our 

 lower internode was 8|, the penultimate 3|, and the ultimate 

 2 1 inches in length ; and the inclination of the whole shoot 

 was such that a circle 19 inches in diameter was swept by it. 

 When the movement ceased the lower internode was 9 and 

 the penultimate 6 inches in length ; so that, from the 27th to 

 the 37th revolutions inclusive, three internodes were at the 

 same time revolving." — (pp. 3, 4.) 



The shoots of many climbers sweep their circles more 

 rapidly than the Hop, the common Pole Bean (^Phaseolus 

 vulgaris} in rather less than two hours, Convolvuluses of va- 

 rious species in the same time or rather less ; while more 

 woody stems naturally move more slowly, some requiring from 

 24 to 50 hours for each revolution. But the thickness or tex- 

 ture of the shoot does not govern the rate, many slender shoots 

 moving slower than some stout ones, and some lignescent 

 quicker than other purely herbaceous ones. The movement 

 apj)ears to be accelerated, up to a certain point, by raising the 

 temperature, or rather is retarded by lowering it ; but while 

 the conditions are nearly the same, the rate is often remark- 

 ably uniform. The quickest rate of revolution of a proper 

 stem observed by Mr. Darwin was that of a Scyphranthus, in 

 77 minutes. When the light comes from one side, the semi- 

 circle towards the light is usually described in less time, often 

 in less than half the time, of that from the light. The ten- 

 dency of young stems to turn toward the light is here active 

 as usual, but is overcome by a superior force. The end of 

 the shoot describes circles or broad ellipses, or else, from in- 

 sufficient power or mechanical disadvantages, narrow ellipses, 

 semicircles, or irregular figures. A horizontal shoot of con- 

 siderable length will thus be found, not unfrequently, to sway 

 from side to side in a semicircular course, while the extreme 

 internodes are making complete revolutions. 



