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. | | 
Deséription In describing a plant, the following details — 
of Stems. should be noticed with regard to the stem : 
— 1. Kind—(a) Underground. - 
° - . (b) Aerial, herbaceous, shrubby, or ds. 
~ 9. Direction. — Upright, creeping, or climbing. 
- 8, Shape.—Square, round, angular. 
4. Colour. 
-5, Branches and their modifications, spines, etc. 
6. Surface. —Smooth or hairy. 
