Ultrastructural characteristics in some species in the order Scytosiphonales

A number of ultrastructural characteristics were observed in three species of the order Scytosiphonales, Colpomenia sinuosa, Petalonia debilis, and Scytosiphon lomentaria. These included the typical phaeophycean thylakoid banding pattern in the chloroplast, prominent pyrenoid lacking thylakoids, pyrenoid sac, strictly perinuclear Golgi bodies, association of outer membranes of the nucleus and chloroplast endoplasmic reticulum, microtubules between the chloroplast double membranes, even distribution of plasmodesmata through the cross walls, and deposits of electron dense material within vacuoles. A comparison of these data to those published earlier on the brown algae indicates a close ultrastructural relationship between the lower orders. The presence of a single chloroplast with a pyrenoid in each cortical and sporangial cell distinguishes the Scytosiphonales. There are a few differences between cells of the field material and cultured sporelings of Petalonia debilis.