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3.1<br />
3.2<br />
3.1 TS of the: petrified stem of the fossil seed fc:m Lygi"opuru. In thIS<br />
Cuooniferou5 plant the same tissue systems excur 35 in pruc:nr-day<br />
flowering plants. The ground tissue is represented by:l. prominent pith (1)<br />
and conex which sho....-s an ourer network of fibres (2). The dennal system<br />
;lnd leaf bases have, however, nor been preserved. The ring of secondary<br />
xylem (3, composed of radially scriatcd tracheids) and the poorly<br />
presrvtd phloem (4) rcpres=t Ihe vascular systo:m. A leaf [race (5) is also<br />
app.arem.<br />
,-----=<br />
62<br />
1 Pith<br />
2 Network of fibr(':$<br />
3 Seconda£)' xylem<br />
4 Phlocm<br />
5 Leaf trace<br />
3.2 Li""m lIsitat;u;mun/ (flax) showing<br />
the distrihution of vascular. ground :lnd<br />
dermal systems in the stem of ,1 dicotyledon.<br />
The laner is composed of a single-layered<br />
epidermis (1) bur the ground system comprises<br />
both the parenchymatous pith (2)<br />
and the cortex (3). The outer limit of the<br />
\·ascular system is marked by large phloem<br />
fibres (4) while internally groups of conducting<br />
elements (5) lie in rhe pbloem<br />
parenchyma. A conspicuous vascular cambium<br />
(6) separates the phloem from the<br />
second.uy xylem (7). (LM x 130.)<br />
1 Epidennis<br />
2 Parenchpnatous pith<br />
3 Cortex<br />
4 Phloem fibres<br />
5 Phloem conducring dements<br />
6 Vascular cambium<br />
7 Secondary xylem
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