But the Handbook of Texas Online has a lot of information. This might be a good start:
http://www.tshaonline.org/handbook/online/articles/DD/wad1.htmlThe summary is that from independence in 1836 until about 1960, the Democratic Party was
the party in Texas. Opposition parties played a role, but after 1905, there weren't any, just internal Democratic factions. This was not the Democratic Party we have today — it was intensely racist and corrupt (there's a party like that today... I forget what it's called... starts with an "R"...)
Anyway, the Democratic nomination process involved a combination of primaries and caucuses, but this combination was routinely "tweaked" to favor some faction or another. The reason why the Republicans aren't saddled with all the rules and regulations is that the Democratic Party was the only political party in Texas from 1905-1960, so the laws governing Democratic nominations were essentially the laws governing the selection of the winners. Thus, the regulations were specifically applied to the Democratic Party, but were optional for minority parties.
One purpose for the system was to exclude blacks. Although blacks could not be legally excluded from the general election, the Democratic Party in Texas managed to exclude them from the primaries for many years. Because there was no opposition, black voting in the general election was irrelevant.
Now that I've learned even more about the history of the TDP, I'm feeling like this complex system should be abolished just to repudiate its origins. Still, it does seem to have some utility in today's world.