In which plant was the importance of day length for flowering first observed?

List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.

Given below is a highly simplified representation of the human sex chromosomes from a karyotype. The genes 'a' and 'b' could be of

The differential equation of all circles which pass through the origin and whose centres lie on the $Y$-axis is

When the temperature of a black body increases,it is observed that the wavelength corresponding to maximum energy changes from $0.26 \mu m$ to $0.13 \mu m$. The ratio of the emissive powers of the body at the respective temperatures is

If the direction cosines of two lines are given by $l+m+n=0$ and $l^2-5m^2+n^2=0$,then the angle between them is