160 REVIEWS. 



many twining stems, such as those of the Hop and the Morn- 

 ing Glory, are apt to undergo. It is plain to see, however, 

 that many stems which revolve do not twist at all ; and those 

 that do never could twist on their axis at every revolution 

 without sjjeedy destruction, — indeed usually do not twist until 

 they have ceased revolving. Every one must have noticed that 

 the growing extremity of a Hop, Convolvulus, or other twiner, 

 when unsupported, hangs over or stretches out horizontally to 

 one side. But it is not so well known that this outstretched 

 portion, wdiile at the proj^er age, is continually sweeping 

 round, in circles widening as it growls, and always in the same 

 direction, in search of some object round which to twine. The 

 Hop revolves with the sun ; the Convolvulus, Bean (Phaseo- 

 lus), etc., against the sun, that is, in the same directions that 

 they twine. Two or three internodes are usually revolving at 

 the same time. Mr. Darwin observed thirty-seven revolutions 

 in one internode of a Hop, — the first revolution made in about 

 twenty-four hours, the second in nine hours, the third and the 

 following ones up to the eighth in a little over three hours 

 each. " The shoot had now grown 3| inches in length, and 

 carried at its extremity a young internode an inch in length, 

 which show^ed slight changes in its curvature. The next or 

 ninth revolution was effected in two hours and thirty minutes. 

 From this time forward the revolutions w^ere easily observed. 

 The thirty-sixth revolution was performed at the usual rate ; 

 so was the last or thirty-seventh, but it was not quite com- 

 pleted ; for the internode abruptly became upright, and after 

 moving to the centre became motionless. I tied a weight to 

 its upper end, so as slightly to bow it, and thus to detect any 

 movement ; but there w^as none. Some time before the last 

 revolution the lower part of the internode had ceased to move. 

 ... It moved during five days ; but the more rapid move- 

 ment after the third revolution lasted during three days and 

 twenty hours. The regular revolutions from the 9th to the 

 36th inclusive, were performed at the average rate of 2 h. 

 31 m. The weather was cold, and this affected the tempera- 

 ture of the room, especially during the night, and consequently 

 retarded a little the rate of movement. . . . After tlie seven- 



