Hormone	Positive Effects	Negative Effects
Ethylene	$\bullet$ Promotes horizontal/transverse growth. $\bullet$ Makes stem positively geotropic. $\bullet$ Promotes apical dominance. $\bullet$ Breaks seed and bud dormancy. $\bullet$ Enhances fruits ripening and root initiation.	$\bullet$ Inhibits longitudinal growth. $\bullet$ Decreases sensitivity to gravity. i.e., root become apogeotropic $\bullet$ Enhances senescence of leaves and flowers, fruits. $\bullet$ Prolongs dormancy of lateral buds. $\bullet$ Mediates formation of ABA under water stressed conditions. $\bullet$
Abscissic Acid	$\bullet$ ABA is used as anti transpirant, by reducesing water requirement and during irrigation (by partial closure of stomata). $\bullet$ Also, induces flowering and root initiation in some plants. $\bullet$ Also, induces flowering and root initiation in some plants. $\bullet$ Used in prolonging dormancy of buds and seeds. $\bullet$ Increases resistance of plants, to cold and other types of stresses thus also known as stress hormone.	$\bullet$ Promotes abscission of flower and fruits. $\bullet$ Stimulates senescence of leaves by stopping protein and RNA synthesis. $\bullet$ Promotes bud and seed dormancy. Retards cambial activity by stopping mitosis in vascular strands and cambium. $\bullet$ Act as antagonist to gibberellins and counteracts the effect of other growth hormones (IAA and cytokinin). $\bullet$ Inhibits seed germination and growth of embryos in them.

Phytohormones are synthesised by plant cells, itself and individually. These are auxin, GA, ABA ethylene and cytokinin. There is not a separate system of their translocation in plants. So, their effects on plants are also inter mixed. e.g., many effects of auxins GA shows the same function. Similarly, ethylene and ABA support each other for many roles in plants. Secondly, effects of phytohormone in vitro and in vivo will also be different.

The phenomenon by which apical bud suppress the growth of lateral buds is known as apical dominance. It is caused due to release of plant hormone auxin from apical duds. It can be overcome either by the spray of cytokinin, that promotes the growth of lateral buds or by trimming of bushes which remove apical buds and allow lateral buds to grow.

The plant hormones are synthesised by the plant cells individually accordingly and when needed. Few hormones are specifically synthesised at a particular plant part, like auxin synthesised in growing shoot apices.

Ethylene is emitted by ripened fruits. Cytokinin is found in dividing cells. Unlike plants animal being more advanced, and organised they have proper hormone secreting glands and organs.

In both plant and animals these are transported through the transport system of their body. In plants, hormones are translocated via xylem and phloem to the site of activity.

Discovery of plant hormone gibberellins was made by chance. It happened by chance in rice fields. A few plants of rice were observed, which were unusually taller than the normal ones. Scientific investigation revealed, that these were infected with a fungus, known as Gibberella fufikuroi. This fungus releases a plant hormone gibberellic acid in excess concentrations which made the plant to grow unusually tall. This compound was later known as gibberellin is hormones present in all plants.

The term used for accidental finding is Serendipity which means fortunate happenstance. It was coined by Horace Walpole in 1754. He explained it as making discoveries, by accident and sagacity, of things, which were hot in quest of.