Phototropism
Gravitropism
The classic experiments
Germination & gibberellin
Practice
lamp position — angle from straight above the shoot
50° to the right
cover the tip — an opaque cap over the tip
cut the tip off
Root laid horizontal
Shoot laid horizontal
Darwin · intact shoot, lit from one side
Darwin · tip removed
Darwin · tip covered with an opaque cap
Darwin · base covered, tip exposed
Boysen-Jensen · gelatin block between tip and stump
Boysen-Jensen · mica sheet between tip and stump
Boysen-Jensen · mica slipped into the shaded side
Boysen-Jensen · mica slipped into the lit side
Went · agar block that held a tip, on one side, in the dark
Went · plain agar block on one side, in the dark
What does this result show?
Run it, then click one.
Whole grain
No embryo + gibberellin added
No embryo, no gibberellin
Dwarf pea + gibberellin
phototropism — auxin crosses to the shaded side and those cells elongate more
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How to think about it
Common mistakes