Cuar. IV. SPIRAL CONTRACTION. 165 
and symmetrical structure has been noticed by several 
botanists, but has not been sufficiently explained.* It 
occurs without exception with all tendrils which after 
catching an object contract spirally, but is of course 
most conspicuous in the longer tendrils. It never 
occurs with uncaught tendrils; and when this appears 
to have occurred, it will be found that the tendril had 
originally seized some object and had afterwards been 
torn free. Commonly, all the spires at one end of an 
attached tendril run in one direction, and all those at 
Fig. 13. 
A caught tendril of Bryonia dioica, spirally contracted in reversed directions. 
the other end in the opposite direction, with a single 
short straight portion in the middle; but I have seen 
a tendril with the spires alternately turning five times 
* See M. Isid. Léon in Bull. wind into a spire, which, since 
Soc. Bot. de France, tom. v. 1858, the tendril is made fast at both 
p. 680. Dr. H. de Vries points extremities, must of necessity he 
out (p. 306) that I haveoverlooked, in some places to the right, in 
in the first edition of this essay, others to the left.” But I am not 
the following sentence by Mohl: surprised that this brief sentence, 
“After a tendril has caught a without any further explanation 
support, it begins in some days to did not attract my attention. 
