you wrote:
>
> The questions that need to be asked are: Under what conditions
> would a particular _Nepenthes_ species produce upper pitchers in
> its native habitat? What purpose does it serve? Is an upper
> pitcher mechanically different from a lower pitcher for trapping
> insects.
That's the case by sure. If you compare ground pitchers and upper
pitchers from many species you see clear parallels though these
species are not all closely related.
Yellowish or green, +/-infundibulate upper pitchers with little or
no red: N. eymai, bicalcarata, maxima (often), treubiana, inermis,
dubia, sumatrana, rafflesiana (sometimes), tomoriana, carunculata,
ovata, insignis, lowii, ephippiata are just some which come spontaneously
to my mind.
Several species which have infundibulate upper pitchers have +/-
globose or cylindrical most often darker (+/- reddish brown) lower
pitchers: N. bicalcarata, tomoriana, treubiana, sumatrana,
rafflesiana, eymai, maxima,.... (see above list ;-))
As I already mentioned they belong to various groups inside the
genus which from my point of understanding can only mean that the
parallels are a sign for completely different prey which has to be
attracted and have developed independently _or_ are a very old
characteristics of the first Nepenthes species which were so
good that they were never changed. Both means that these are
important characteristics. On the ground you have ants, termites and
many other small crawling creatures. BTW the lower pitchers ease the
way to the deadly fluid by their fringed wings.... The upper
pitchers have to attract flying creatures (=> they have to show
different colours and shapes.
> Different species of insects trapped,
Some seem to be quite specialised: In the upper pitchers of N.
insignis (Irian Jaya) we found exclusively winged cockroaches!
The finding of cockroaches suggests that these pitchers attrack night
active insects.
> different nutritional values (N levels), different amounts of light in the
> upper part of the trees, different humidity?
I doubt that it's different levels of nutrients. I feel that the
problem is more simple (;-)):
When the plant grows larger it cannot count on ants anymore and small
(young) plants cannot count on flying insects which rarely if ever
would visit a ground pitcher. Both pitchers were optimized during evolution
to catch a maximum of prey.
> Also, has anyone ever tried grafting a mature _Nepenthes_ scion onto a root
> stock of another _Nepenthes_?
I tried once but did not succeed. It would be interesting to read if
anyone here knows how to do it.
All the best
Andreas
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