Cuap. I. TWINING PLANTS. 11 
remains straight ; but with twining plants every part 
of the revolving shoot has its own separate and 
independent movement. This is easily proved; for 
when the lower half or two-thirds of a long revolving 
shoot is tied to a stick, the upper free part continues 
steadily revolving. Even if the whole shoot, except 
an inch or two of the extremity, be tied up, this part, 
as I have seen in the case of the Hop, Ceropegia, 
Convolvulus, &e., goes on revolving, but much more 
slowly ; for the internodes, until they have grown to 
some little length, always move slowly. If we look to 
the one, two, or several internodes of a revolving shoot, 
they will be-all seen to be more or less bowed, either 
during the whole or during a large part of each revolu- 
tion. Now if acoloured streak be painted (this was 
done with a large number of twining plants) along, 
we will say, the convex surface, the streak will after 
a time (depending on the rate of revolution) be 
found to be running laterally along one side of the 
bow, then along the concave side, then laterally on 
the opposite side, and, lastly, again on the originally 
convex surface. This clearly proves that during the 
revolving movement the internodes become bowed 
in every direction. The movement is, in fact, a con- 
tinuous self-bowing of the whole shoot, successively 
directed to all points of the compass; and has been 
well designated by Sachs as a revolving nutation. 
As this movement is rather difficult to understand, 
it will be well to give an illustration. Take a sapling 
and bend it to the south, and paint a black line on the 
