Possible Clues:

• Bush, perhaps, angry initially about secret service
• Gum-yielding shrub
• It grows for a century after a century to start with
• Tree source of gum
• Tropical tree, inc. mimosa, wattle
• Flowering tree/shrub of Australia and Africa
• It takes at first a doubel century to grow this
• After a century a matter of intelligence becomes a thorny matter
• Area agents maintaining air-conditioning plant
• Shrub of warm climates