Invicta dark and clear grow bell set invicta 118600 p the invicta dark and clear grow bell set allows children to perform experiments comparing the effect of light and dark on plant and root growth the clear grow bell is be used to show how light can affect the germination and subsequent growth of roots and seedlings in light the dark grow bell shows the effect on the same events in complete darkness the lids and bases are interchangeable so that light on roots and dark on seedl