In my home tank the ambulia brances when it hits the surface. In the school tank, cooler temps, lower nitrates, it branches near the base. It also displays the reddish color all along the stem that I see in my home tank after the growth has hit the surface.
As for light temperature, the home tank has a pair of 9325K 55 watts on the back and 6500K 55 watts on the front. The school tank has 9325K NO flourescent tubes.
The school tank has been running for 4 weeks with no nitrate at all, but for root suppliments, and those were added only this week. The CO2 level in the school tank is much lower than the home tank, near 5ppm vs near 20ppm. Oh, maybe that is it, maybe it grows long internodes at higher CO2 levels? That is how the submerged conditions at school resemble surface conditions at home, creating submerged growth at the school that looks like surface growth at home where surface Co2 levels ought to be closer to 5ppm than 20 ppm lower in the tank.
Hmm, thinking back, it may be that the growth earlier, before I cranked up the CO2 a bit more, was slightly more compact.... I thought it was because I trimmed and left bases to grow instead of topping and replanting last time, but maybe that isn't the cause of the thinner, longer growth!