SPIRAL TORSION. 323 
but more commonly form a single continuous line; 
when arranged in leaf-whorls it generally happens 

Fic. 173.—Stem of Galiwm spirally twisted. From a specimen com- 
muuicated by Mr. Darwin. 
that some of the leaves are turned downwards, while 
others are erect. It has been said that this condition 
occurs particularly frequently in plants growing in 
damp places. It is certainly true that spiral torsion of 
the stem is specially frequent in the species of Hqui- 
setum, most of which grow in such spots. In these 
plants either the whole of the upper part of the stem is 
thus twisted, or a portion only: thus Reinsch’ cites 
a case in Hquisetum Telmateia, where the upper and 
lower portions of the stem were normal, while the 
intermediate portion was twisted spirally. In this 
instance the whorl next beneath the spiral had twenty- 
eight branchlets, and that immediately above it thirty. 
Along the course of the spire there were two hundred 
and three; dividing this latter number by the mean of 
' « Flora,’ Feb. 4, 1858, p. 69, tab. ii, f. 3, and also ‘ Flora,’ 1860, p. 737, 
tab. vii, f. 9. 
