I'd say no, because it became defiled, perverted, and outside of BM. The Hist may share one mind, but as Mere-Glim has said, some of the Hist can go rogue. Since this one was, what it seemed, forcibly removed, and known to be defiled and perverted, I highly doubt it would be making those commands. If it did, I highly doubt the leader of the BWC and those harvesting the Hist (who were all argonians) would have done what they did to it.

I really believe that, as far as the Blackwood Company goes, Ri'Zakar was the true mastermind and was simply using the powers of the Hist to his advantage. As a Khajiit, the Hist wouldn't speak to him anyway. He either didn't understand its true nature and abilities or didn't care. He simply wanted that sap to power up his warriors and make him a wealthy man.

oops, thought Jeetum-Ze was the head. Meh, well it still doesn't matter that much, a bunch of the high ranking officers were argonians, and the tree didn't seem to yell "HELP ME! SON OF A, HELP ME!"

The points you raise seem to indicate that the compulsion comes out of the roots. If BWC Hist had been semi-recently transplanted, then its roots probably wouldn't go all that deep.

I still want to know what you guys' opinions on the City-Tree's action are. Did the City-Tree separate itself in order to condemn all of the local foreign-tainted Argonians, or was the City-Tree separated by the other Hist in order to protect the larger herd and then because its own opinion on foreign Argonians was low and decided to act the way it did because it didn't have to bow to the larger herd/the herd had condemned it to death.

P.S. What is a large group of trees? A forest?

A large group of trees - a forest. In the case of the Hist, I'd say a semi-independant collective.

As for the City-Tree's actions, I'd say it was seperated by the other Hist for its' opinion.

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Speaking of collectives, this makes me wonder; are all Argonians under the control of the Hist? Or is the control just stronger among those who live in the black marsh?

I don't think "control" is the right word, at least most of the time. They are 'aware" of the Hist, even when far away, but are always connected because Black Marsh is connected. However, it is implied that they get harder to hear over great distances, so the bond may be stronger, but outside of particular circumstances they aren't exactly like some kind of possessing demon.