Hygrophilia Growth

[Billinet at aol_com]

Hello,

My hygrophila has been growing vertically for over a year, requiring periodic 
clippings.  However, starting about a month ago, some of it started growing 
horizontally, putting down roots at each node that anchored and began 
producing plantlets.

What causes this?   One archived message says that this is a normal response 
to good light and nutrients; another says that it shows that the plant is 
under stress.

The tank is a low tech 29 with 2 WPG and an occasional Flourish feeding.  
Other plants are doing OK.

Thanks.

Bill