100 
HISTOLOGY OF VEGETABLES. 
spiral fibres are uniformly coiled from right to left, 
but in some instances, this is reversed, and left-handed 
spirals are found, as in the section of a Palm from the 
East Indies, Fig. 84, g, h ; it has been suggested that 
the direction of the fibre may determine that in which 
the plant coils round an upright pole. The Hop , which 
exhibits these left-handed spiral vessels is also a left- 
handed climber, which gives support to the above- 
mentioned theory. 
Whilst speaking of fibres unrolling spirally, I take 
the opportunity of showing a fact I have lately made 
out, that even membrane itself may occasionally be 
met with, that will tear and unroll spirally. Botanists 
FIG. 87. 
Hairs from the fruit of Cycas revoluta unrolling spirally. 
