Optical principles
Compound microscopes use two lens systems: objective (4×, 10×, 40×, 100× oil) and eyepiece (usually 10×). Total magnification = objective × eyepiece.
Lighting and contrast
Adjust iris diaphragm — too much light washes out unstained tissue; too little reduces resolution. Kohler illumination aligns light path for even brightness.
Structures to identify in leaf cross-sections
- Upper epidermis — often one cell layer with waxy cuticle.
- Palisade mesophyll — columnar cells packed with chloroplasts.
- Spongy mesophyll — irregular cells with air spaces for gas exchange.
- Vascular bundle — xylem (water transport) and phloem (sugar transport).
Oil immersion (100×)
Apply single drop of immersion oil on coverslip, rotate 100× objective into oil contact. Clean oil immediately after use to protect lenses.