Application of cryo-ultramicrotomy techniques to microtubules of bracken (Pteridium aquilinum L.) sperm cells.

Mature antheridia from agar cultures of prothalli of the bracken fern were fixed for short periods of time in buffered 1% glutaraldehyde. Cryosections were obtained after rapid freezing in glycerol. In oblique cryo-sections through flagella rows of small globular subunits were observed making up each axoneme, the approximate size of each globule was 4.5 nm. Other superficial material was also found in the same sections. In transverse sections through the layer of microtubules which surround the helical nucleus, subunits of the order of 4.5 nm were observed.