166 TENDRIL-BEARERS. Cuar. IV, 
in opposite directions, with straight pieces between 
them; and M. Léon has seen seven or eight such 
alternations. Whether the spires turn once or more 
than once in opposite directions, there are as many 
turns in the one direction.as in the other. For 
instance, I gathered ten attached tendrils of the 
Bryony, the longest with 383, and the shortest with 
only 8 spiral turns; and the number of turns in the 
one direction was in every case the same (within one) 
as in the opposite direction. 
The explanation of this curious little fact is not 
difficult. [will not attempt any geometrical reasoning, 
but will give only a practical illustration. In doing 
this, I shall first have to allude to a point which was 
almost passed over when treating of Twining-plants. 
Tf we hold in our left hand a bundle of parallel strings, 
we can with our right hand turn these round and 
round, thus imitating the revolving movement of a 
twining plant, and the strings do not become twisted. 
But if we hold at the same time a stick in our 
left hand, in such a position that the strings become 
spirally turned round it, they will inevitably become 
twisted. Hence a straight coloured line, painted along 
the internodes of a twining plant before it has wound 
round a support, becomes twisted or spiral after it has 
wound round. I painted a red line on the straight 
internodes of a Humulus, Mikania, Ceropegia, Con- 
volvulus, and Phaseolus, and saw it become twisted as 
the plant wound round a stick. It is possible” that 
the stems of some plants by spontaneously turning on 
