[dmforcier]

Ron, get yourself a magnifying glass. My eyes aren't terrible, but I still do all my seed work under a glass, with tweezers.

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Perlite - volcanic foam which is useful in that it does not absorb water, but holds air to provide oxygen to the roots.

Vermiculite - manufactured material that retains water and reportedly a little air. I've never found it useful in my situation, but many do use it, especially in hot climates.

The quantities in a growing medium aren't that important; both are chemically neutral. IME effectiveness depends greatly on the consistency of the other components and the watering regimen. In a soil that cycles quickly between wet and dry, perlite may not make a difference. But in soil that sometimes is saturated for days (e.g. rainy spells) that oxygen may be important. At any rate, Al's 5:1:1 recipe has perlite making up 1/7 of the medium. In your greenhouse, I wouldn't consider it necessary at all.

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When growing under domes under lights or sunlight, be careful of the temperature inside the dome. I place a thermometer inside until I get it stabilized in a good range - low 90s F is the hottest I want. Mid-80s is better.