Revue internationale d'écologie méditerranéenne International ...

Treatment Species
H 2SO 4 Refrigeration
H 2SO 4
Refrigeration
Incubation
Scratching
ecologia mediterranea, tome 29, fascicule 2, 2003, p. 153-164
INTERPRETING GERMINATION RESULTS BASED ON SEED SIZE, MASS AND ECOLOGICAL… ◆
Artemisia monosperma Del
Calligonum comosum L.
Deverra tortuosa (Desf.) DC.
Juncus acutus L.
Ranunculus sceleratus L.
Bidens bipinnata L
Cucumis prophetarum L
Salvia lanigera Poir
Asphodelus tenuifolus Cav.
Crepis bulbosa (L.) Tausch
Amaranthus paniculatus L.
Carduus getulus Pomel.
Citrullus colocynthis (L.) Schrad
Eleusine indica (L.) Gaertn
Euphorbia granulata Forssk.
Euphorbia helioscopia L.
Forsskaolea tenacissimaL
Kickxia aegyptiaca (L.) Nabelek
Peganum harmala L
Polypogon viridis (Gouan.) Breistr.
Cleome amblyocarpa Barratte & Murb
Cyperus capitatus Vand
Lygos raetam (Forssk) Heywood
Polygonum equisetiforme Sm.
Table 3. Treatments applied for breaking dormancy used in the laboratory experiments
for some of the studied species
the soil surface. It is well known that these gravels serve
not only to protect the underlying soil from water and
wind erosion but also reduce moisture loss. Classification
of the natural habitats from which the seeds of the present
investigation were collected is presented in table 2. Nine
habitats are arranged according to their moisture availability.
The habitat of fallow fields attained the highest
water holding capacity (76.14% ± 4.01) followed by that
of canal banks (66.24% ± 3.08). The soil reaction (pH)
in the habitats of the study area was generally alkaline,
where the value ranged from a maximum of 8.61 in the
saline soil to a minimum of 7.2 in the rocky cliffs and
stony soil. Concerning the soil texture, three soil types
were distinguished: loamy sand (five habitats); sandy clay
loam (two habitats) and sandy soil (two habitats).
Twenty-four plant species out of the sixty-six studied
species were treated to break dormancy and to promote
germination (table 3). Twelve of the treated species which
attained highest germination percentage when incubated
at 28-32 o C in the laboratory were those collected from
the wadis (shallow gullies draining from northward to the
sea, where a drainage system collecting water in amount
that could be much greater than the recorded rainfall) or
fallow fields. On the other hand, plant species containing
mucilage materials on their seed coat or had leathery or
woody coat were treated with H 2SO 4. In general, seeds
of Cleome amblyocarpa, Citrullus colocynthis, Lygos raetam,
and Calligonum comosum were the hardest to germinate.
Some of the morphological variabilities in the seed
form, shape and size of the studied species are illustrated
in figures (1-3). As cited by many authors (e.g.
Mayer and Poljakoff-Mayber, 1980; Baskin & Baskin,
1998) adhering fruit structure covers the dispersal units
(seeds) of some families (e.g. Cyperaceae, Polygonaceae
and Umbilliferae). These figures also show some of the
characteristic seed dispersal structures such as the woolly
structure surrounding the seeds of Forsskalea, the two
retrorsebarbed bristles of Bidens achen, the pappus of
simple hairs of Carduus, the woolly appearance of Cleome
seeds and the tuff appendages of Calligonum.
The mean seed size (mm) of the sixty-six species in
this study as shown in table 1 are ranged from a minimum
of 0.028 mm for Reseda decursiva collected from sand
dune and 0.029 mm for Pulicaria arabica collected from
rocky cliffs and stony soil to a maximum of 23.89 mm for
Silybum marianum collected from canal banks. Seed mass
ranged from a minimum of 0.155 mg for Pulicaria arabica
collected from rocky cliffs and stony soil to a maximum of
42.704 mg for Pergularia tomentosa collected from wadis.
It is worthy mentioned that freshly harvested seeds of
most perennials were kept for a period of time before
germination can take place.
Generally, the germination percentage of seeds germinated
in Petri dishes was notably higher than that germinate
in pots under half and full water supply. Furthermore,
germination on filter paper was relatively rapid and was
completed in 2-5 days. However small seeded plants
emerged radicles earlier than large seeded plants.
The studied species were divided into two group
based on their life forms; annuals, represented by 36
plant species (table 4) and perennials represented by 30
plant species.
Results of germination under different water regimes
(table 4) showed that at increasingly favorable moisture
conditions the difference between small and large seed
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