Assertion: cactus's rib | /r/CapableOf | play important role
Facets:
value: in retention
type: PURPOSE
value: in water storage
type: LOCATION
Source sentences:
text: Cactus tubercles and ribs play an important role in water storage and retention, as they allow the stem to expand to increase the volume of moisture it can hold without stretching or bruising and then retract as the stem loses water, which minimizes the amount of surface area that’s exposed to direct sunlight.