188 PHARMACEUTICAL BOTANY 
shedding cork in layers; obconical, or having the shape of an 
inverted cone; flexuous or bent; tortuous or twisted; truncate, or end- 
ing abruptly, as if cut across at the summit. 
Stem MobpirIcaTIONs. 
Twining stems are those which coil spirally around a support, 
as the stems of the Hop, Bittersweet, Dodder, etc. 
Tendriliform stems are those which undergo thread-like modi- 
fication and become sensitive to contact of a side branch or other 
Cette Prins object, coiling around it, as in 
es Passion flower, Grape, Squash, 
Cle. 
Spines are formed by the 
oF Leaves 
a 
checking and hardening of a 
(f ))) : branch that may then become 
wo, }f| + sity Buds defensive, as in hawthorn, 
ie honey locust, etc. 
Aerial tuberous stems are those 
in which one or more inter- 
eee & nodes enlarge above ground 
— and store reserve food, as in 
Fic. 118.—Diagram of a longitudinal pseudobulbs of orchids. 
section through the tip of astem. 1, 2, Subterranean tuberous stems 
3, 4, successively older beginnings (pri- 
are those in which an under- 
mordia) of leaves. (Mottier.) 
ground stem or branch enlarges 
as a food-storing center: (a) annual type, tuber, as in potato, etc., 
corm, as in crocus, etc.; (b) perennial type, bulbs as in lily (scaly) 
and onion or hyacinth (tunicated). 
Phylloid stems or phylloclades are green, flat, leaf-like stems in 
which flattening branch expansion has occurred, as in Asparagus, 
Ruscus, etc. 
Cactoid stems are those in which reduced, condensed branches 
or stems become swollen for water (and food) storage, as in Cacti, 
some Euphorbia species, etc. 
ABOVE-GROUND OR AERIAL STEMS.—A twining stem winds 
around a support, as the stem of a bean or Morning Glory. 
A culm is a jointed stem of the Grasses and Sedges. 
A climbing or scandent stem grows upward by attaching itself 
to some support by means of aerial rootlets, tendrils or petioles. 
Examples: Ivy, Grape, etc. 
