Define immigration and emigration .

A biologist studied the population of rats in a barn . He found that the average natality was 250, average mortality 240, immigration 20 and emigration 30. Calculate the net increase in population .

Define variations.

Emigration is:

Define Humification.

Define: Distillation

Define aestivation.

Define stem.

Define Pitch

Define fermentation.

Define conservation.