macrocyst is

[Pref. macro-, and Mod. Lat., ., cyst is.] Botany : A genus of Fucacese, family or tribe Lamina ride. Macrocyst is pyrifera is a giant sea weed, with a stem 700 feet long, no thicker than the finger. The branches are as slender as packthreads; the leaves long and narrow, each has at its base a vesicle filled with air, enabling the plant to float. It is met with in the ocean in the south temperate and south polar zones.