Page 19 - 11-Bio-9 Kingdom plantae

9. Kingdom Plantae eLearn.Punjab

Class Filicineae

The Filicineae or fems are mostly shade and moisture loving plants. A very few are able to live
under dry conditions. They grow on the hills and in plains. Some are epiphytic and grow on the bark
of trees. Although ferns are worldwide in distribution, they are especially abundant in the tropics.
They vary greatly in size. Important ferns are Dryopteris, Pteridium, Adiantum and Pteris etc.

Adiantum (Maiden-hairfern)

Adiantum is a fem that grows along moist walls and water courses. It is a small herb consisting of
stem, roots and leaves. Stem is a short, thick and underground, usually unbranched horizontally
growing rhizome. The rhizome is protected by brownish scales (ramenta) and covered by persistent
leaf basis. Fibrous adventitions roots arise from the lower side of the rhizome. Large, pinnately
compound fronds arise from the upper side of rhizome. Young leaves (fiddle heads) show circinate
vernation. The stipe (stalk) and rachis are black, smooth, shiny (hence called maiden hair fem).
The leaflets (pinnae, and pinnules - leaflets of second order) show dichotomous venation. Sori
(groups of sporangia) are born on the underside of reflexed lobes of the margins of leaflets, and
are protected by bent margin of the leaflet, forming false indusium.

Life Cycle : Life cycle of Adiantum shows hetromorphic alternation of generation, sporophyte

being dominant and gametophyte small and reduced but separate and independent. The diploid
sporophyte produce large number of sori (singular-sorus).They are green, but when ripe they
become dark brown. Each sorus consists of a number of sporangia covered by false indusium. The
leaves bearing sporangia are called sporophylls.

Each sporangium is slightly flattened, biconvex body (capsule) born on a multicellular stalk. The
capsular wall consists of a single layer of flat, thin walled cells. The edge of the capsule is made up
of two parts, the annulus and the stomium. The annulus occupies three fourth of the edge and
remaining one fourth is the stomium. Annular cells have their radial and inner walls thickened.
The stomial cells are thin- walled. Inside the sporangia, haploid spores are formed by reduction
division, from diploid spore mother cells. The annulus of the sporangium contracts in dry weather,
the stomial cells being thin-walled rupture and spores are dispersed by wind.

When a spore falls on a moist soil, it germinates at a suitable temperature and produces a haploid
gametophyte or prothallus.

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