Thanks,
@Wires_Guy_wires, but the simple act of cutting/slicing causes growth to initiate? Pruning in winter has no such effect.
Ordinary tissues will develop some degree of cold hardiness when exposed to a sequence of deepening chills as normally occur in fall. Why would a new graft not do likewise?
Apparently (to me) there is something in the nature of damage response that leads to a new graft being inherently unable to develop hardiness just as the growth from a newly pruned root apparently is unable to develop hardiness as can the new growth on an 'untouched' root.
But, otherwise, thanks for your intelligible explanation.
When you prune, hard or soft, you keep most of the messaging system intact, except in the parts that you've cut off. Think of it as an ant colony; if you remove a few, the colony is going to act the same. If you cut the colony in half, it's going to act more or less the same. Pick twenty ants from a colony, and they'll not behave as a colony.. until they've found a queen and have the ability to function as a colony again. The - so to speak - governing body of a plant decides where it's going. If a cutting or graft is not connected to that body entirely, it might behave different. Plant messaging, just like animal messaging, relies on feedback loops. If there's nothing talking back, either because it's not connected or because it's dormant, then there's no loop. Well, actually there is, but it's limited to the scion itself.
Not all plants do this to a similar extent. I own a mugo pine that I've tortured over a year ago, and it flushes continuously, even throughout winter. To my knowledge junipers for instance don't give a hoot if there's a governing body or not. But in deciduous plants, it's seems to be more or less a ground rule that if the arms aren't attached to the spine, they don't function. I
think the reason to those differences are found, at least for a little, in the fact that most deciduous plants have a harder time compartmentalizing their body and thus having a harder time to created their own fully functioning feedback loops.
I think bleeding is one thing to keep in mind as well. Plant tissue can expand and retract (is that the right word?) to some extent. But in fresh growth, there's usually so much water that the expansion limit is exceeded with just a few degrees below zero. Fruits, being both high in sugars but also very high in water content, turn to slush after you've frozen them. It's not because they're not hardy, it's just that the water itself expands more than the cells can take.
In damaged parts, expanding water (due to lower temps) can expel itself through the vascular system. If water can escape freely, there's no need - or possibility - for expansion. A damaged carrot will dry out faster in the fridge compared to an intact one. But both are dormant and both have the frost-protective materials flowing inside them. They're both perfectly hardy, but since they're stationary, the damaged one doesn't heal either; it continues bleeding either until the wound has dried up and closed itself, or until growth resumes and fixes the place up.
Am I still making sense? It's been a long day today. Sorry for that.