Plant Growth and Development

The seeds of many temperate plants, such as apple, peach and cherry, do not germinate until they have been exposed to a period of chilling.
Stratification is the treatment in which seeds are kept at a low temperature (about 0 to $10^\circ C$) under moist conditions for some weeks.
During this treatment the level of inhibitors such as abscisic acid falls and that of gibberellins rises, so dormancy is broken.
Scarification is the weakening or breaking of a hard seed coat by mechanical or chemical means.
Vernalisation is a low temperature treatment that promotes flowering, not the breaking of seed dormancy.
Chelation is the binding of metal ions by organic molecules.
So the treatment is called stratification.

Parthenocarpy is the development of a fruit without fertilisation; such fruits are seedless.
Normally the growth of the ovary into a fruit is stimulated by the auxins and gibberellins produced by the developing seeds after fertilisation.
If the unpollinated flowers are sprayed with low concentrations of auxins (such as IAA or NAA) and gibberellic acid, the ovary is stimulated to grow into a fruit without fertilisation.
This is how parthenocarpic (seedless) tomato fruits are produced.
Simply removing the androecium (emasculation) prevents self-pollination but does not make the ovary develop.
Vernalisation promotes flowering, and phenylmercuric acetate is an antitranspirant that closes stomata.
So parthenocarpic tomatoes are produced by treating the plants with low concentrations of gibberellic acid and auxins.

In most higher plants the growing apical bud inhibits the growth of the lateral (axillary) buds. This phenomenon is called apical dominance.
It is caused by the auxin synthesised in the shoot apex, which moves downward and suppresses the lateral buds.
In pruning, the shoot tips are cut off (decapitation), which removes the source of auxin.
The axillary buds are thus freed from apical dominance and grow out into lateral branches.
With repeated pruning more and more branches develop, and the hedge becomes dense and bushy.
The same principle is used in tea plantations.
So pruning makes the hedge dense because it frees the axillary buds from apical dominance.

The endosperm of a barley grain stores food mainly in the form of starch, which the embryo cannot use directly.
When the seed imbibes water, the embryo produces gibberellic acid (GA).
GA diffuses to the aleurone layer and induces it to synthesise and secrete hydrolytic enzymes, the most important being $\alpha$-amylase.
$\alpha$-amylase hydrolyses the starch of the endosperm into maltose and glucose.
These soluble sugars are absorbed by the scutellum and supplied to the growing embryo, so germination proceeds.
This is used in the malting of barley in the brewing industry.
So the enzyme that can stimulate the germination of barley seeds is $\alpha$-amylase.