Bio Investigatory
Bio Investigatory
Bio Investigatory
Bio Investigatory
Bio Investigatory

Bio Investigatory

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  • 7Dispersal of Seeds


    Project: Study of dispersal of seeds by aarious agencies

    tntroductionThe flowers of angiosperms form fruits from ovary and seeds from ovules after pollination andfertilization. As seeds'contain the embryo, or the future plant, their dispersal is important formaintaining the continuity of species through generations and for the establishment of plants a!different lolations. h many pl-,jts, the fruits anJseeds have certain special features with the help ofwhich they are distributeioiver considerable distance from the parent plant. After gefting favourableconditions, they germinate and give rise to new plants'

    Wind, water, animals and explosive mechanisn are the main agencies tha! h91p in the dispersal ofseeds. Some seeds are light and &spersed by wind. The seeds which are slightly heavy develop wings.Some develop hooks, hiirs, spines, which enable them to stick to the fur of animals and are thus getcarried fromtne place to *oih"r. The various agencies for seed dispersal and the characteristics of theseeds they disperse are as follows.

    Agencies for dispersal

    Wiilil Water AnimalsmechanismI


    r. Ho

  • Biology Lab Manual for Class 12

    Procedure1. Collect various types of seeds from your neighbourhood and study them for fheir modes of

    dispersal.2. Cttthe fleshy fruits and observe their seeds. Study and find out their mode of dispersal.

    ObservationsRecord the following:

    (i) the external aPPearance of the seed,(ii) the size of the seed,(iii) the weight of the seed,(iv) the presence of outgrowths like spines, hooks, wings, hairs, etc',(v) the type of fruit, if available,(vi) the occurrence of the seed, in a pod (legume) or in a capsule,(vii) identification of the seed, i-f possible,(viii) other special features.

    On the basis of above characters, identify the agency through which the dispersal of the seed takesplace.

    In the next few pages some description about fhe agencies of seed dispersal and the specificfeatures of the seeds they disperse are given for your convenience'

    Dispersal of seeds by wind The wind is probably the most important agency of seed dispersal innature. Seeds have dispersal by wind following features.

    L. Lightweight and minute seeds Some seeds are so light that they are blown by air like dust, e.g., seedsof orchids, grasses, etc.

    Z.Wings The seeds of some plants like Moringa, Cinchonat, Oroxylum, etc., have wings. Th9 ry:ngs Teth'r, diy, light and membran6us, due to which these seeds are easily caflied away to long distances bythe wind.j. Hairs The seeds ol Calotropis, Gossypium (cotton), etc., possess hairs which help them to float in airand eventually carry them to long distances.

    4. Batloonlike appendages In some plants, certain floral parts become inflated, which keep the fruits orthe seeds floating in th; air, e.g., Plrysalis, Colutea, etc. In Physalis, the persistent calyx is inflated like aballoon.S.pappusandparachutemechanisrr [r the members of Asteraceae (Compositae) like Taraxacum,,"pui"' are modified into tufts of hair called pappu! *_hiol, persistent and Jound attadred tosiigle-seeded fruits. The pappus forms a miniature umbrellalike white outgrowth which acts like aparachute that allows the wind to carry the seeds to great distances.

    6. Censer mechanism hr some plants lke Argernone mexicana (prickly PoPpy), Aristolochia, Papaoer(poppy), etc., fruits,rupture after maturity fui the seeds do not come out' When the fruit is shaken"iol^eniiy

    by the wind, the seeds get scattered in all directions.

    7. persistent styles In plants like Clematis, Naraaelia, etc., .the,style of the flower persists with the fruitand becomes hairy which hetp in their dispersal.


    _:, ;:{ jB. Rolling mechanism or twmble weeds Some wild herbs like Amaranthus albus, Chenopodium albumiett.,get detaihed from soil when dry, and roll over the ground due to the force of wind. \Atrhile doing sothey scatter seeds all along the way.

    9. propeller outgrowths The fruit of Ailanthus possess propeller outgrowths due to which they arepropelled to a long distance.




    Dispersal of Seeds











    @.{'+. ,



    Fig.7.1 Dfferent types of fruits and seeds showing adaptations for their dispersal by wind

  • Biology I"ab Manual for Class 12

    Dispersal of seeds by water Water is another agency for the dispersal of fruits and seeds, mainly foruqriti. plants growing near the river banks or seashores'7. Eloating iteoices Thefruits and seeds of some plants develop some kind of floating devices such asthe fibrous growth on the outer coverin g of cocos"nucifta (coconut) or the sPongy structure inNelumboiucyero(btfis). 11 ur" ,t*"tores protectihe fruit and help it to float on water'2.Water-tesistantprotectioecoaering The outermost layer of some fluits is smooth, waxy andimpervious to water, as in coconut. :


    B.Lightseeits The seeds of sonneda"t" ltkeNymphaea (water lily) are small and light, and containair-filled aril which keep them floating in water'

    Fibrous oulercovedng

    C*cas nuc$era{Coeonut}

    ireiufftbo rlrcif*ra {Lstus}

    Eig.72 Fruits showing adaptations for their dispersaf by water

    Dispersal of seeds by animals The various adaptations for dispersal of fruits and seeds by animals areas follows.l. Stick7 frltits anil seeds Many plants produce sticky fruits_or seeds which adhere to the feet or beakof birds and are kansported from one place to another, e.g., Boerhaaoia, Cleame, etc'

    2. Haokeit fruits anil seeds Many fruits and seeds have spines, hooked bristles, stiff hairs, thoms, etc',

    to attaclr themselves to the skin, fur, or wool of the roaming animals or human beings, e'g',Xmtthium'Aclryranthus,Tribulus, Aristida, etc. iS. ia*U l*fts The edible fruits are consumed but the seeds being resistant to digestive enzymes- comeout with the faeces of the animal , e.g., Ficus bmghalmsis (banyao), F . religinsa (peepal), gu1ya, ap|!e, etc,fuig" ,".a, are thrown away after ionsuming"the juiry and'flet"hy p*il e'g', mango, litchi' etc' Nuts ofoak (Quercus), chestrut, ut"., ,t" often collecied by rodeitts T{ ftuy hide these dry seeds at differentpla"""-wh"r. some of the seeds germinatd. under suitable conditions.

    Disperialof seed$bllexplosivemechanism ftr6 its$f some plants sudi 1s lm?atims (balsam)'vlr{r: G*rri;*, .1",.-b;;;th sudden jerk due to whic-h the'seede are in all directions. Thep;{;

    "t;r;*il,l"A*+"iolentty with a "i""tir,g sound: rn.Eibsllium elatariutn (sqtrirtins cucumber), the

    ir,,go" pressure within ttre fruit, after maturifu, canse-s it to burst at the poiit of attadrment of thep"iicet. Rs a result, the,seeds come out like a fountain along with a mucilaginous mass'


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    Dispersal of Seeds


    Hooks SPines




    )Gnthiua Adtyfinthus







    Ecballium elaartum

    Fig,7,4 Different types of fruits and seeds with adaptations for their dispersal by explosive mechanism