4 MR. DARWIN' OX CLTMBIHG TT.AIS'TS. 



twenty-seventh revolution our lower internode was 8|, the penul- 

 timate 3|, and ultimate 2| Laches in length ; and the inclination 

 of the whole shoot was such, that a circle 10 inches in diameter 

 was swept hy it. When the movement ceased, the lower inter- 

 node was and the penultimate 6 inches in length ; so that, from 

 the twenty-seventh to thirty-seventh revolutions inclusive, three 

 internodes were at the same time revolving. 



The lower internode, when it ceased revolving, became upright 

 and rigid; but as the whole shoot continued to grow unsupported, 

 it became nearly horizontal, the uppermost and growing inter- 

 nodes still revolving at the extremity, but of course no longer 

 round the old central point of the supporting stick. Prom the 

 change in the position of the centre of gravity of the revolving 

 extremity, a slight and slow swaying movement was given to the 

 long and horizontally projecting shoot, which I mistook at first 

 for a spontaneous movement. As the shoot grew, it depended 

 more and more, whilst the growing and revolving extremity turned 

 itself up more and more. 



With the Hop we have seen that three internodes were at the 

 same time revolving ; and this was the case with most of the plants 

 observed by me. With all, if in full health, two revolved; so 

 that by the time one had ceased, that above it was in full action, 

 with a terminal internode just commencing to revolve. With 

 Hoya carnosa, on the other hand, a depending shoot, 32 inches in 

 length, without any developed leaves, and consisting of seven in- 

 ternodes (a minute terminal one, an inch in length, being counted), 

 continually, but slowly, swayed from side to side in a semicircular 

 course, with the extreme internodes making complete revolutions. 

 This swaying movement was certainly due to the movement of the 

 lower internodes, which, however, had not force sufficient to swing 

 the whole shoot round the central supporting stick. The case of 

 another Asclepiadaceous plant, viz. Ceropegia Gardnerii is worth 

 briefly giving. I allowed the top to grow out almost horizontally 

 to the length of 31 inches ; this now consisted of three long inter- 

 nodes, terminated by two short ones. The whole revolved in a 

 course opposed to the sun (the reverse of that of the Hop), at rates 

 between 5 h. 15 m. and G h. 45 m. for each revolution. Hence, as 

 the extreme tip made a circle of above 5 feet (or 62 inches) in dia- 

 meter and 1G feet in circumference, the t ip travelled at the rate 

 (assuming the circuit to have been completed in six hours) of 32 

 or 33 inches per hour. The weather being hot, the plant was 

 allowed to stand on my study-table; aud it was an interesting 



