Biology Today - February 2018

• A plant can be (i) monoecious - if male and female flowers develop on the same plant, HJmaize, castor or (ii) dioecious
  
  
  • if male and female flowers borne on separate plants, HJ., mulberry, date palm. When more than two types of flowers
    bisexual, male and female develop on the same plant it is called polygamous HJ, $FHUUXEUXP,
  
  
  
  


• When male and bisexual flowers are present on the same plant, it is called andromonoecious, HJ9HUDWUXP.


• When female and bisexual flowers are present on the same plant, it is called gynomonoecious, HJplants with heterogamous
  head inflorescence in Family Asteraceae.


• Calyx and corolla together constitute accessory floral whorls. Depending upon the presence or absence of these whorls flower
  can be:

(i) Achlamydeous : Accessory floral whorls are absent, HJ3LSHU

(ii) Monochlamydeous : Only one accessory whorl (either calyx or corolla) or perianth (a collective term given to a group of
undifferentiated calyx and corolla), is present, HJ3RO\JRQXP (Polygonaceae), onion (Liliaceae).

(iii) Dichlamydeous : Both the accessory whorls are present, HJ +LELVFXVURVDVLQHQVLV

• In some plants, thalamus shows distinct nodes and internodes. The internode between calyx and corolla is termed as
  anthophore, H.J., 6LOHQH; that between corolla and androecium, the androphore, H.J.,3DVVLIORUD and that between
  androecium and gynoecium, the gynophore or gynandrophore, H.J., &OHRPH.


• Sometimes thalamus is prolonged into gynoecium to form a central axis and is called carpophore, H.J., coriander.


• A floral bud like a vegetative bud is either terminal or axillary in position.


• Arrangement of sepals, petals, stamens and pistil, etc., on the thalamus is the same as that of the leaves on the stem or
  the branch, LH., alternate, opposite or whorled.

Relative Position of Floral Organs on Thalamus

• There are three forms of thalamus as regards the insertion of pistil and androperianth (other floral organs) YL]., hypogyny,
  epigyny and perigyny.

Table: Differences between hypogynous, perigynous and epigynous flowers

Hypogynous flower Perigynous flower Epigynous flower

(i) The upper part of thalamus is slightly

swollen and forms a cushion like disc.

The upper part of thalamus may be disc

shaped, cup-shaped or flask-shaped.

The upper part of thalamus is usually

flask-shaped or tubular.

(ii) Calyx, corolla and androecium arise

below the level of ovary.

Calyx, corolla and androecium arise from

around the ovary and not beneath it.

Calyx, corolla and androecium arise

from above the level of ovary.

(iii) Ovary is superior while all other floral

parts are inferior.

Ovary is half-superior/half-inferior. Ovary is inferior while all other floral

parts are superior.

(iv) The gynoecium is placed at the top of

the thalamus. The wall of ovary is not

fused with the thalamus.

The ovary is placed at the bottom of cup

or flask-shaped thalamus. Ovary wall is

not fused with the thalamus.

The ovary is completely inserted and

the wall of ovary is fused with the

thalamus.

(v) Calyx, corolla and androecium remain

separated from the gynoecium so that

the ovary is visible from outside.

Stamen

Thalamus

Superior

ovary

Petal

Sepal

Calyx, corolla and androecium often

develop from a common base. The ovary

of gynoecium may or may not be visible

from outside.

Stamen

Thalamus Sub-inferior

ovary

Petal

Sepal

Calyx, corolla and androecium

develop jointly from the neck of

hollowed out thalamus so that the

ovary is not visible from outside.

Stamen

Thalamus Inferior ovary

Style

Petal

Sepal