Mark you posed an interesting question. I'd like to hear the answer to this as well. You might get a better response if you post it on the propagation from cuttings forum.
Karyn

Hi Mark
As Karyn says a very interesting question. First of all the natural process is for all of us, animals or plants to be born, reproduce, age and die. Species such as edulis have been selected for their ability to produce a large crop of fruit within the first few years of planting. The strain of all the reproduction ages it early. Other wild Passiflora species however - especially the tree Passiflora, are much longer lived - possibly up to 100 years but no one really knows. See the link below for more information. There are hybrids from the early 1800's like the violaceas still going strong. Plant genetics is immensely complex see http://www.passionflow.co.uk/passiflora-passion-flower-flowering-genetics.htm for information just re flowering. I think that you are quite right that a cutting - whether from hybrid or species, which generally will be from the last few feet of new growth will give the plant a fresh start. In other words plant can naturally have immortality by cloning which scientists are only now beginning to manage with animals.
Myles

Here is a link that might be useful: Passiflora lifespan

Theoretically, a plant can be cloned repeatedly forever without end. However, plants that get propagated through cuttings for many, many years, will have a tendency to drift, and many new "sports" may arise with new characteristics. These can be due to genetic mutations that occur within a single cell that then gives rise to a shoot with different properties, or more likely, occurs because of subtle changes in the expression of various genes, which are referred to as epigenetic changes. So, if the same cultivar has been repeatedly cloned for a very long time, it may no longer be identical to the original plant.

Thanks Myles--fascinating stuff! For some reason, when I was thinking of a "reset" mechanism the whole idea of telomere shortening and senescence never crossed my mind. However, with animals (especially cloning) I guess I would generally think of the telomeres in a single cell or maybe a group of cells regenerating (my knowledge here is also a bit weaker than I'd like...). In a plant cutting I take it this must happen throughout all of the cells--or certainly at least those that are actively growing and dividing--even in distant regions of the cutting? I should do some reading--I'm a bit ignorant on this point.

I hope that the agencies that fund telomere-related research in areas such as cancer and aging also fund work on plants. No doubt the two systems complement one another.

BTW Myles, P. tripartita var. mollissima survived 99 F/37 C yesterday. It's "only" 87 F/ 30 C now (12:30 P.M.) and tomorrow's high is forecast for 77 F/ 25 C. Luckily our heatwaves are brief (unlike Pasadena where I used to live). I did see the Tacsonias at GG Park in S.F. a few days after it hit 97 earlier in the year and they also looked fine--and were in bloom.