The moon.
Curl is the rotation of wind field
you just curl it however you want you dont need to have curly hair to curl your hair its actually sometimes easier to curl your hair if your hair is straight
Sagittal
Cold weather can cause citrus leaves to curl and so can water stress. Aphids are another cause.
The tree has a fungal disease.
most likely aphids, though there may be many reasons
Sunlight causes this.
aphids
Stink bugs
Because whatever you Are using to heat this up however Causes the peperonis to curl up and get small very easy.
stunted plants leaf curl up as a cup shape hard leaf midrib yellow leaves
It causes the Bourdon tube to straighten.
New leaf growth is caused by the cold soil causing the leaf to curl and fall off producing a new leaf. The cause of the leaf to curl can be from an aphid species or different plant diseases.
A general answer ( since you did not specify what plant ) is insect damage, drought, or soil is too alkaline.
The homophone for "curl" is "kurl."
You can use un-, for uncurl.
we curl the leaves and thats the curl