58 
ESSENTIALS OF BOTANY 
of the hop (Fig. 30); others, 
as the morning-gl 
ing the opposite course.1 
76. Underground Stems. 
— Stems which lie mainly 
or wholly underground are 
of frequent occurrence and 
of many kinds. ; 
In the simplest form of 
rootstock (Fig. 31), such as 
is found in some mints and 
in many grasses and sedges, 
the real nature of the creep- 
ing underground stem is 
shown by the presence 
upon its surface of many 
scales, which are reduced. 
leaves. Rootstocks of this 
sort often extend horizon- 
tally for long distances in 
the case of grasses like the 
sea rye grass, which roots 
itself firmly and thrives in 
shifting sand-dunes. In 
the stouter rootstocks, like 
Z. that of 
the iris 
(Fig. 82) 
Fie. 31. Rootstock of Cotton-Grass (Eriophorum). and the 
1See Strasburger, Noll, Schenk, and Karsten’s Text-Book, pp. 257-260; 
also Vines, Students’ Teaxt-Book of Botany, London and New York, 1894, 
pp. 759, 760. 
