Chap. IY. 



SPIRAL CONTRACTION. 



165 



and symmetrical structure lias 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. Loon in Bull. 

 Soc. Bot. de France, torn. v. 1858, 

 p. 6>-0. Dr. H. de Vries points 

 out (p. 306) that I have overlooked, 

 in the first edition of this essay, 

 the following sentence by Mohl : 

 "After a tendril has caught a 

 6upport, it begins in some days to 



wind into a spire, which, since 

 the tendril is made fast at both 

 extremities, must of necessity be 

 in some places to the right, in 

 others to the left " But I am not 

 surprised that this brief sentence, 

 without any further explanation 

 did not attract my attention. 



