[Galin]

Legate of Amon Lanc wrote: ... If I understood it correctly, you (maybe just rhetorically) ask how would Treebeard know the reason why the Uruk-hai (like Uglúk) do not fear the light. But he says it. If we presume it was the Uruk-hai whom Treebeard saw, he saw them roaming the forest at day, which of course seemed strange to him. But as he says, "these Isengarders are more like wicked Men". This means that he had to notice something "mannish" on them.

Not necessarily something beyond 'sun tolerance' though. In other words, even if the Uruk-hai are the beings in question, they are like Men in that they do not mind the Sun, yes, but why don't they mind it, specifically? Treebeard doesn't know, he doesn't have certain knowledge. Are they ruined Men? half-breeds? some other reason maybe? some 'spell' perhaps? would even a half-breed automatically not mind the Sun? He doesn't ask all these questions, but he is questioning.

Treebeard's reason to suspect something about the Isengarders appears to concern the Sun, which, as far as he knows, is unusual for Orcs. Call it interpretation A.

If I understand your post correctly (and maybe I don't), you seem to be suggesting something like: Treebeard says they are more like wicked men because there is something 'mannish' about them and he saw them in the day and this also seemed strange to him (adding to his reasons to say they are like wicked men).

Maybe

The ultimate question, however, leads again to what exactly he saw. But the point is, that all these goblin-faced Men made the impression that they are Men. Even Merry, though he said they were unbelievably Orcish, classified them as Men. To make the judgement he did, Treebeard must have thought to himself: "Ha, here are some Orcs!" and only on the second sight "But hey, there is something strange on them, which is not quite Orcish."

Coupled with (from an earlier post, see above)...

'... but I'd presume that for someone like Treebeard with his long lists and ages of knowledge, he'd speak more clearly of "wicked Men" and not "man-like Orcs", had he seen these "goblin-faces".

In other words (if I read this right) you're suggesting that Treebeard can't have seen half-orcs because they give the general impression of Men and he would have spoken more clearly in your opinion. So you conclude he saw the Uruk-hai and etc.

Again maybe, but not clearly so in my opinion.

'if I had seen you before I heard you, I should have just trodden on you, taking you for little Orcs, and found out my mistake afterwards' Treebeard to the Hobbits

I rather think it quite likely that if Treebeard saw orkish beings, due to what he thinks about Orks and darkness he then wonders about 'ruined Men' or some result of interbreeding. Also I think one can press this point about classification too much. If indeed Treebeard saw beings who were (to use your words) 'unbelievably Orkish' we can't certainly know he wouldn't generally think them orkish enough to be termed 'Orcs' (when speaking to the Hobbits).

Treebeard's commentary here might suggest to some that the Uruk-hai are more than 'Orc-folk' with respect to blood, but as I say that is one interpretation, and but part of the evidence.

In any case The Ent might be surprised to know that the Uruk-hai (boast as they like) are not the only Orcs who can run 'well enough' under the Sun.