se a Aes, Le Wace OAL pe Lads tha \ Wood 
‘ 
The External Form of Plants. — 77 
dies off every year, as in Salvia officinalis, the stem 1s suffru-_ 
ticose. .In palms and some other trees the trunk is simple 
and unbranched, and is then a caudex; when the stem— 
remains weak and does not 
become woody, it 1s erbaceous, 
and then but rarely, as in 
many succulent cacti, is per- 
ennial. The scafe is a leaf- 
less stem bearing only flowers, 
springing from a flat base, or 
belonging to a so-called stem- 
less plant ; it may bear only 
a single flower as in the tulip, 
or several as in the lily-of-the- 
valley (Fig. 108), hyacinth, 
and Plantago. The culm is a 
stem the internodes of which »,,, 
are separated by thickened _ lily-of-the-valley, Convallaria  ma- 
: _  Jsealis (reduced). 
nodes, as in grasses, and 1s 
usually hollow and unbranched ; the ca/amus on the con- 
trary, as in rushes, is pithy and without thickened nodes. 
Sometimes, as in the strawberry, the stem sends out runners, 
z.e. branches which run along the ground, put out adven- 
titious roots from their 
nodes or at their extre- 
mity, and develope there 
a perfect plant. 
If a stem is cut through 
)/ ) = 
Yy 
ff 
Yj iff 
Fic.109.—Sec- Fic.110.——Sec- F1G.111.—Sec- 
transversely, the figure of tion of trian- tion of square tion of 5-rib- — 
gular stem. stem. bed stem. 
thie section is usually more 
or less round or cylindrical, or is compressed into an elliptical — 
form; but it is often angular, for instance triangular in 
Carex (Fig. 109), square in Labiate (Fig. 110), five-ribbed 
(Big tir), &c: 7 
The form of the stem is usually more or less cylindrical, 
but often globose, two-edged, as in several species of Cactus, 
PD a) "4 A@ , . 
f ey t & 4 gr ia “ rim 
NV nt ; ie, ‘AM Reet Lhe , Tey 7 i 4 
108. — Rhizome and scapé of the ~ 
