58 ELEMENTS OF BOTANY 
of the hop (Fig. 80); others, 
as the morning-glory, tak- 
ing the opposite course.’ 
76. Underground Stems. 
—Stems which le 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 
_: _/_ that of 
SSS XT the iris 
a (Fig. 32) 
Fie. 31. Rootstock of Cotton-Grass (Hriophorum). al a the 
1See Strasburger, Noll, Schenck, and Karsten’s Tewe(-Book of Botany, 
pp. 281-284, Macmillan, New York; also Vines'’s Students’ Tert-Book of 
Botany, pp. 759, 760, London and New York, 1894. 
