How were different plant growth regulators discovered?

(N/A) The discovery of all five major groups of plant growth regulators occurred largely by accident.
Discovery of Auxin:
This was the first growth hormone to be discovered. Observations of canary grass coleoptiles showed they responded to unilateral illumination by growing towards the light source (a phenomenon known as phototropism). After a series of experiments,it was concluded that the coleoptile tip was the site of production of a transmittable influence that caused the bending of the entire coleoptile. The first $PGR$ in the auxin group was isolated by $F.W. Went$ in $1928$ from the coleoptile tips of oat seedlings.
Discovery of Gibberellins:
In the early $20^{th}$ century,the 'bakane' (foolish seedling) disease of rice was reported to be caused by a fungal pathogen,$Gibberella$ $fujikuroi$. Symptoms included elongated stems and little or no grain production,leading to weak plants. It was later identified that the active substance was gibberellic acid. The Japanese plant pathologist $E. Kurosawa$ reported that uninfected rice seedlings developed these symptoms when treated with sterile filtrates of the fungus.
Discovery of Cytokinins:
$F. Skoog$ and his co-workers,while studying the nutritional requirements of tissue culture derived from tobacco stem internodes,observed that the callus (a mass of undifferentiated cells) proliferated only when the nutrient medium was supplemented with extracts of vascular tissues,yeast,coconut milk,or $DNA$. It was later found that the active substance was a modified form of adenine,which was crystallized and identified as kinetin. Compounds exhibiting kinetin-like properties were termed cytokinins.
Discovery of Abscisic Acid:
During the mid-$1960s$,three independent researchers reported the purification and chemical characterization of three different inhibitors: inhibitor-$B$,abscission $II$,and dormin. Later,all three were proven to be chemically identical and were named Abscisic Acid $(ABA)$.
Discovery of Ethylene:
$Cousins$ $(1910)$ confirmed the release of a volatile substance from ripened oranges that enhanced the ripening of stored unripened bananas. This volatile substance was later identified as the gaseous plant growth regulator,ethylene.