ONE AND TWO PLANES. “When restricted to one plane or orientation, unbranched filaments can be formed (e.g. Spirogyra); when confined to two orientations, cell division can give rise to branched filamentous, monostromatic, or pseudo-parenchymatous tissue constructions (e.g. Stigeoclonium, Volvox and Ralfsia, respectively).”
http://aob.oxfordjournals.org/content/85/4/411.full.pdf