Oblivion:Seeking Your Roots

Quick Walkthrough
# Harvest Nirnroot for the first time to be given a new quest. You should ask an alchemist about it.
# Question alchemists to get no useful information other than to see Sinderion in Skingrad.
# Find Sinderion in his cellar at the West Weald Inn in Skingrad. Ask him about Nirnroot, and he'll tell you a story.
# He tells you to collect a certain number of Nirnroot which you should return to him. He'll tell you to wait 24 hours that so he may finish his research. When he's done, he rewards you with a potion, and you should repeat the process three more times.
# When you've gone through this a total of four times, he'll have exhausted his research, and from now on he'll just pay in gold for any Nirnroot that you should return to him.

Detailed Walkthrough
A Word on Nirnroot
Nirnroot is a very noticeable, vibrant, greenish-blue plant with four large leaves, usually located close to water and emitting a quiet ringing noise.  There are hundreds of locations where the plant can be found, but unlike every other plant in the game it does not regrow; each plant can only be harvested once.  As a result, it is considered to be a rare plant.  Details on where the plant can be found are provided on the Nirnroot page.

When harvested for the first time, a new quest will be added with the information that the plant is very rare and that you should consult an alchemist about it.  This quest will also be added if you talk to Sinderion (see below).  Ask about Nirnroot.  In the inventory the ingredient is shown to have no value (likely to represent that its value is unknown).

Best Botanist in Cyrodiil
When asked, alchemists are stumped by this ingredient and will suggest that you go see Sinderion in Skingrad, who is said to be the best botanist in Cyrodiil.

Sinderion can be found in his cellar at the West Weald Inn. When you select the dialogue topic "Nirnroot", he will tell you a lengthy story that boils down to a powerful potion called Elixir of Exploration and will mark Shadeleaf Copse on your map, where three sprigs of Nirnroot can be harvested.  He gives you a note describing the plant and its location, and asks you to collect enough plants so that he can make some of the elixirs.

Each time you bring him a set of Nirnroot, he devises a new, more powerful elixir that he can make... but only if you can go collect even more Nirnroot plants.

Nirnroot Samples
At each of the four stages of this quest you will repeat the following steps:
#Sinderion will ask you to collect a number of nirnroots (first 10, then 20, 30, 40) so that he may create a variant of the elixir.
#Once you bring him the desired number of Nirnroot sprigs, select the "Elixir of Exploration" dialogue topic for him to take the sprigs.  He tells you to wait for 24 hours to finish his research.
#When he's done with the research, he will reward you with one bottle of his new elixir and tells you to bring more Nirnroot.
#An additional bottle of the new elixir is available for purchase from him each time you speak with him. It respawns in his inventory like a usual non-unique item (e.g., arrows).

The quest ends after you have brought Sinderion the last 40 (total 100, which is one third of all the plants in Cyrodiil) sprigs of Nirnroot. He says that he has exhausted his research regarding the Elixir of Exploration. But if you find more Nirnroot in your travels, he will be happy to buy it from you (at least 10 samples of Nirnroot each time).



Results
Finishing this quest results in Sinderion's disposition skyrocketing to 100, and haggling becomes fairly easy. Your mileage may vary, but it's a good place to off-load collected ingredients and potions that you don't need.  This can be helpful if you're not an alchemist or a user of a lot of potions, especially since the fields around Skingrad are a very ingredient-rich area.

Strategy
You need 100 Nirnroots to complete the quest, but there are over 300 in Cyrodiil. Searching on the shores of the major bodies of water will get you to your goal relatively quickly. Searching around the Topal Bay in the Blackwood area, both sides of the Niben Bay and the lower/upper Niben, and Lake Rumare (both the outer and the island shores) will net you more than enough Nirnroots to complete the quest. Simply start on one side of the Bay, work your way up to and around Lake Rumare, and back down to the other side of the Topal Bay.

Notes
Nirnroot emits a faint, pulsating noise. This sound is very useful in locating nirnroots in unfavorable conditions.
While most outdoor bodies of water host a Nirnroot, there are a small few that do not.
More often than not, the location of a Nirnroot is in relation to a landmark in its immediate vicinity. This landmark may be a structure, cell, or natural object (such as a rock or a tree). For instance, many Nirnroots are located near the notable parts of bridges, such as the ends or supports.
Nirnroot does not always grow directly beside the edge of water. For instance, if a beach is particularly wide, it may be found throughout its breadth. 
Most of these rules do not apply to the Blackwood area. Nirnroot is very common there, growing in different and quite random places near water, but sometimes 50-100 feet away from it, often in clear view and without any specific reference point.  
Bodies of water inside caves/forts will sometimes host a Nirnroot.
Many houses of upper class citizens contain potted Nirnroots; similarly, they may be found in many quest-related houses and areas. Picking a potted Nirnroot, even while in clear view of someone, is not a crime.
If the small island you just visited has no Nirnroot by its shores, it will be located right in its middle.
Nirnroot never grows in groups. About the only areas where Nirnroots grow remotely close to each other are around the walls of Leyawiin, Shadeleaf Copse and the swamps by Fieldhouse Cave. Some islands carry more than one Nirnroot, but no shrine, ruin, cave or such has more than one. 
The best time to search for Nirnroot is during the day when the weather is sunny and clear. Fog makes it hard to see, rain makes it hard to hear, and thunderstorms make it difficult to both see and hear Nirnroot.
 You can slide the "Grass Distance" bar to zero (far left) under Video options.  This makes searching for Nirnroot much easier: since the Nirnroot plants are considered objects (not foliage), they will continue to be visible, while grass and other ground plants will not be rendered.  You can also use the console command "tg" which means "Toggle Grass" to achieve the same effect.
It is not possible to duplicate Nirnroots with either the identical scroll glitch or the magical chest in the Arch-Mage's chamber.
After you have turned all 100 samples of Nirnroot in to Sinderion, thus completing the quest, you can continue to give him Nirnroot samples ten at a time, in return for which he will give you 250 gold. However, if you are a Master Alchemist it is actually more profitable to turn the Nirnroots into Drain Health poisons, which have a base price at their highest quality of 56 gold each, as opposed to the 25 gold Sinderion gives you for each Nirnroot sample.
If you wish to barter with Sinderion, do so before you give him a batch of Nirnroot. Once you have given him the Nirnroot, he will tell you to return in 24 hours to receive your potion and break off conversation. If you attempt to converse with him again before 24 hours have elapsed, he will tell you to come back later and break off conversation once more, thus rendering it impossible to barter with him until he has finished the elixir.

Bugs
The messages that appear in the game keep track of how many Nirnroots you have picked so far, not how many Nirnroots you have in your possession.  For example, while hunting for 20 Nirnroots you will get the message: "I've found 20 more of the Nirnroot, I should return to Sinderion in Skingrad..."  However, if you have lost a Nirnroot (left it in a chest that resets, dropped it, eaten it, etc), you may only have 19 in your possession.  In this case you would need to keep looking despite what the message says, because Sinderion only cares about how many Nirnroots you have in your possession when you talk to him.

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