Who isolated auxin from tips of coleoptiles of oat seedling?

During germination,the stem grows upward and the root grows downward because:

Which of the following is $NOT$ an effect of $Auxin$?

In plants,the precursor of auxins is:

When does the formation of the abscission layer occur?

After a series of experiments,it was concluded that the ....$A$.... of coleoptile was the site of transmittable influence that caused the bending of the entire coleoptile.