~+ 
- 
THE STEM IDEY, 
___ mechanical tissues have been developed. The rigidity produced 
__ by the turgor of the parenchyma cells is particularly useful in 
maintaining the form of the younger parts of herbaceous and 
climbing stems. It is of little or no help in dicotyledonous stems 
that have developed a mas- 
sive column of wood. 
















SLPS) 
pes 
Parenchyma cells serve Sen IIS 
: Meeee eee, 
for the slow conduction of SRS , 
hy <> aR TAIT 
water and food. In the case REL 
Me octax of ats NG, 
of the cortex of the stem it Gog Sea 
F A SP RSO OA) OEY) 
is evident that the water Ye @ aes oWen eeceees 
: : . TO IB ea LIS & O/T 4 $ 
which is received by the pence i = Mine Adal 
TH Seite an | 
collenchyma and the epi- ni ete li: i {| TH 
4 SS eee HTT | TAN) ELLE 
dermis must be conducted 4 sf ( sell: A BAL | A 
bats Si Sse aE 
through the parenchyma. 5 f Sie \B2: | TA | 
: {|__| 4 Eee THEE | a | ; 
The parenchyma is the | i STS BBS WHA | |: } ! 
A . al = |= BS EH} 
special storage tissue of [| 1) Sel = SIMBA || ‘A 1 
| LU | eA eS ASH WHA | Ve 
plants. In general the pa- | 1, 1S 22|| AW WAI RE tC 
4) HSIEH IT F i 
renchyma of the cortex is |, \, SIE ES | | | f | 
less important than the SEIS : 
p  Sv_q pu, ¢_St_,8¢ poss_pe_co ¢ 
parenchyma of the stele as ¥ ph pe c 
a food-storage tissue, but Fic.116. Diagrammatic combined cross 
food is frequently stored and longitudinal sections of stem 
In-it to some extent. p, pith; z,xylem ; sv, spiral vessel ; av, an- 
Collenchyma. On the in-  nular vessel ; pv, pitted vessel ; ¢, cambium 
side of the epidermis there Suite ph Bae st plore gabe i Be, pe 
GSuscally a band of collen- 71, Slreuehyme ry, pernchyma 
chyma (Figs. 118-115). of cortex; co, collenchyma ; e, epidermis 
The cells of the collen- 
chyma are modified parenchyma cells with cellulose walls thick- 
ened at the angles where three or more cells are in contact 
(Fig. 25). The collenchyma resembles parenchyma in being alive 
and in having a moderate amount of protoplasm. The chiet 
function of collenchyma cells is to serve as strengthening mate- 
rial in succulent organs which do not develop much woody tissue, 
or in the soft young parts of woody plants before stronger tissues 

