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Anatomy 75

and form a loop around and under this flagellum. R1 forms the base of attachment of numerous
microtubules running towards the posterior end of the cell, with cytoskeletal function (Figure 2.49).
As yet no complete analysis of the flagellar root systems of Xanthophyceae exists. The typical
root system as presently understood appears to consist of three different types of structures: a des-
cending root originating near the basal bodies, resembling the rhizoplast in extending from the basal
bodies along the nuclear surface, between the nucleus and the Golgi body, but differing in being
unbranched, and in consisting of a succession of rectangular blocks rather than fibers as in the Chry-
sophyceae; a cross-banded fibrillar root composed of slightly curved bands, originating together
with, but at right angles to the descending root, and terminating at the cell membrane; microtubular
roots in various number near the basal bodies, each of which containing three or four microtubules.
In Vaucheria the system is completely different; neither a descending root nor a cross-banded fiber
are present, but its anterior protrusion is supported by a single broad microtubular root of 8–9
microtubules arranged in a row. This root originates near the base of the anterior pleuronematic
flagellum, and from here passes forward along the cell membrane to the tip of the protrusion,
turns around and runs back on the opposite side of the cell, again along the membrane.
Only few data are available on the flagellar roots of Eustigmatophyceae. Both microtubular and
cross-banded fibrillar types are present. The microtubular structures, consisting of 2–5 microtu-
bules, arise close to the basal bodies and pass anteriorly and posteriorly in the cell. The cross-
banded roots are narrow and pass from the region of the flagellar bases along the anterior flattened
face of the nucleus.

FIGURE 2.49 Root system of Ochromonas sp. (Heterokontophyta). LF, long flagellum; SF, short flagellum;
R1, R2, R3, and R4, microtubular roots; RHP, rhizoplast; and N, nucleus.