A two-way growth of 'beard' (3)
I believe the answer is:
awn
'beard' is the definition.
(both can mean a growth on plants)
'a two-way growth' is the wordplay.
'two-way growth' becomes 'wn' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'wn'='AWN'
'of' is the link.
Can you help me to learn more?
(Other definitions for awn that I've seen before include "Stiff bristle on grasses" , "Beard of plant" , "Bristle on grass spikelet" , "Beard of cereal" , "Bristles" .)