Meaning of nagaru

I know that 流れる (nagareru) it's something like "to flow", but what's the meaning of 流る? I saw it once on a music (the verse was さらさら流る) and I can't understand why it doesn't have the "re".

I know that there is an old word that goes 流るる (nagaruru) which means the same thing as 流れる (nagareru). Sometimes this old word is used to make the sentences (be it in lyrics or literature) sound distinctive. In this case the meaning of the word 流る (I assume "nagaru") is the same as "nagareru," but I imagine this was chosen just to be "different" :)

Simply, nagaru is the final form (shushikei) of the classical verb nagaru, which is in Modern Japanese nagareru. The classical nagaru belongs to the Shimo-nidan type of verbal conjugation.
It conjugates as below:
nagare(zu)
nagare(te)
nagaru
nagaruru(kumo)
nagarure(ba)
nagareyo

It seems to me that this fragment of verse “sara sara nagaru” is a part of the famous song “Haru no ogawa” every Japanese know.
This kind of pseudoclassical style was very common in the songs (not only for children but for adults) which were made between the Meiji period and the end of the World War II.

Thank you guys, you really helped me on that!