26 ELEMENTARY BOTANY 
Whilst the stem is revolving, it also becomes spirally 
twisted on its own axis. The Hop twists three times whilst 
making thirty-seven revolutions. The amount of twisting 
seems to depend chiefly on the nature of the surface up which 
the plant is climbing. Darwin allowed Kidney-beans to run 
up stretched string or smooth rods of iron and glass, and 
found that they were much less twisted than when they had 
climbed up rough uneven sticks. 
Description In describmg a plant, the following details 
of Stems. should be noticed with regard to the stem : 
1. Kind.—(a) Underground. 
(o) Aerial, herbaceous, shrubby, or woody. 
. Direction.—Upright, creeping, or climbing. 
. Shape.—Square, round, angular. 
Colour. 3 
. Branches and their modifications, spines, ete. 
. Surface.—Smooth or hairy. 
> Cr 9 DO 
