Cell membrane function and difference-digieduco

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  Functions of cell membrane : (a) The proteins and enzymes present in the cell membrane helps in the transport of certain substances like sugar, sodium and other ions etc. across the cell membrane. (b) Cell membrane protects the internal structures of the cell and different organelles of the cytoplasm. (c) It maintains the shape of the cell. (d) It acts as a selective permeable membrane because it allows to pass certain substances while others are not, hence it helps in the transport of selective materials from and to the cells. (e) The membranes on the cytoplasmic organelles and nucleus most probably formed from the plasma membrane. (f) Other important functions of cell membrane of the cells are endocytosis and exocytosis . Endocytosis is the process by which materials are transported into the cells by the formation of vesicles. It includes two processes-phagocytosis (cell eating) and pinocytosis (cell drinking). The reverse process of endocytosis is exocytosis. During this p
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DEFINITE OR CYMOSE INFLORESCENCE AND ITS TYPES-DIGIEDUCO

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DEFINITE OR CYMOSE INFLORESCENCE.

In cymose the growth of the primary axis is checked and is thereby terminated by a flower young flowers occur below it. In this type flowers open basipetally or centrifugally (in case of fleshy rachis).


DEFINITE OR CYMOSE INFLORESCENCE AND ITS TYPES-DIGIEDUCO

Cymose inflorescences are of following types.

(i) Solitary terminal or Axillaryflower-In this type, apical or axillary bud develointo a single flower e.g. Hibiscus rosasinensis (Malvaceae). This type is included within cymose type as further development is suppressed.

(ii) Monochasium or Uniparous cyme-In this type, the primary axis ends in a flower and one lateral branch is produced ending in a flower and the . process is repeated. There are two kinds of uniparous cyme, such as :

(a) Scorpioid cyme or Cincinnus-In this type, the primary axis with alternate suppression of lateral flowers bearing secondary axes results in a zigzag structure. The family Boraginaceae is characterised by this inflorescence. Examples-species of Heliotropium of the family Boraginaceae, Ranunculus bulbosus (Ranunculaceae) etc.

(b ) Helicoid cyme or Bostryx-In this form, the primary axis with one sided successive
suppression of lateral secondary axes forms a helix. ExamplesHamerocallis flava (Liliaceae), Hamelia patens (Rubiaceae), Myosotis palustris (Boraginaceae) etc.

(iii) Dichasium or Biparous cyme-In this the primary axis terminates into central flower which opens first ; at the base of the primary axis, a little distance behind the apex, two lateral branches bearing flowers arise. Each lateral branch may again give rise to flowers in the same manner. Examples-species of Jasminum, Nyctanthes (Oleaceae) and some members of Caryophyllaceae (Dianthus chinensis).

(iv) Polychasium or Multiparous cyme-This type of inflorescence results when the primary axis terminates in a flower and produces behind the apex more than two lateral secondary axes in a whorled manner. Examples- sambucus nigra, viburnum sp. , calotropis sp. Of Asclepiadaceae etc.

Special types of condensed cymose inflorescence-
(i) cyathium- it is a compound cyme, characteristic of the species of Euphorbia, pedilanthus, etc. of the family Euphorbiadeae. In this case the receptacle terminates into a smgle female flower consisting of tricarpellary gynoecium only, this again is surrounded by numerous male flowers each of which consists of single stamen-these male flowers
are again arranged in scorpioid cyme. The whole inflorescence is surrounded by a glandular involucre containing nectar.

(ii) Venicillaster-It is a compound cyme, characteristic inflorescence of the family Labiatae. In the axils of opposite leaves at hrst a dichasium is produced, then each branch of the dichasium passes into a cincinnus. The flowers are almost sessile and the axes are so short that the flowers are crowded round the stem. So a verticillaster consists of a simple biparous cyme and scorpioid cymes. Examples--Species of Leonurus, Coleus, Ocimum, Leucas, etc. of the family Labiatae.

(iii) Hypanthodium- The inflorescence hypanthodium is composed of three fused primary axes or rachis of closely placed cymes ; as a result of such fusion a cup shaped fleshy concave receptacle almost or
completely closed structure with a small opening at the apex results. The unisexual flowers (three types, e.g. male, fertile female and sterile female) are arranged all over the inner surface of the receptacle in cymose groups. Example-Ficus cunea (Moraceae).
DEFINITE OR CYMOSE INFLORESCENCE AND ITS TYPES-DIGIEDUCO

(iv) Coenanthium-This is found in Dorstenia sp. (Moraceae) where the receptacle is more or less flat with little upwardly curved margins ; minute flowers are embedded within the receptacle.

(v) Cymose capitate or Cymose head-When the flowers develop on a suppressed globular rachis in a cymose manner to form a capitate or head-like structure, it is called cymose capitate. Example-Anthocephalus indica (Rubiaceae).



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