What does $ICBN$ stand for?

$Nicotiana$ $sylvestris$ flowers only during long days,while $N.$ $tobacum$ flowers only during short days. If raised in the laboratory under different photoperiods,they can be induced to flower at the same time and can be cross-fertilized to produce self-fertile offspring.
What is the best reason for considering $N.$ $sylvestris$ and $N.$ $tobacum$ to be separate species?

In which book did $Linnaeus$ present the outline of plant classification?

The study of the kind and diversity of organisms and the existing relationship among them is called

Into how many classes did Linnaeus classify plants?

Who defined species as a group of interbreeding organisms that are reproductively isolated from other such groups?