The N. ampullaria plants, with upper pitchers, that I have seen were all in
lowland areas. Two botanists had seen such plants in Brunei growing in an area
that had high-tension wires overhead and hypothesized that the electrical field
might have caused the upper pitchers to be expressed. (Clarke and Moran in
Malayan Nature Journal, vol 47, 1994) .
The ones that I have seen in southern Peninsular Malaysia were not near
high-tension wires. I did look at an area about three kilometres near these
plants with upper pitchers that was under high-tension wires. However, the few
N ampullaria plants under the high-tension wires did not exhibit any upper
pitchers.
Regards,
Wee Kiat.