Step 1: Understand the two styles:
Ikebana is the Japanese (Eastern) art of flower arrangement.
The Western style is a mass or bouquet type of arrangement.
Step 2: Difference 1 - number of flowers:
Ikebana uses few flowers and leaves, with a lot of empty space.
The Western style uses many flowers packed close to give a full look.
Step 3: Difference 2 - form and meaning:
Ikebana follows line and asymmetry. It is built around three main lines that stand for heaven, man and earth.
The Western style is mostly symmetrical and geometric, and stresses colour and mass.
Final Answer:
Ikebana uses few stems, with open space and asymmetrical line design; the Western style uses many flowers in a full, symmetrical mass.