STEMS 75 
common wax-plant of the greenhouses sometimes describes 
a five-foot circle, the tip moving at the rate of thirty-two 
inches per hour.t This circular motion results from 
some cause not yet fully understood by botanists.? 
The direction in which twiners coil about a supporting 
object is almost always the same for each species of plant, 
but not the same for all 
species. In the hop it is as 
Fic. 41.— Coiling of Petiole of Dwarf i 
Tropzolum. Fig. 42.— Twining Stem of Hop. 
shown in Fig. 42. Is it the same as in the bean? in the 
morning-glory ? 
91. Underground Stems. — Stems which lie mainly or 
wholly underground are of frequent occurrence and of 
many kinds. 
In the simplest form of rootstock (Fig. 43), such as is 
1See article on Climbing Plants, by Dr. W. J. Beal, in the American 
Naturalist, Vol. IV, pp. 405-415. 
2 See Strasburger, Noll, Schenk, and Schimper, Text-Book, pp. 258-262 ; 
also Vines, Students’ Text-Book of Botany, London and New York, 1894, 
pp. 759, 760. 
