Differentiating spermatocytes have been examined in a diploid culture of Pteridium gametophytes. Spermatogenesis is similar to that in haploid antheridia. Although the nucleus of the diploid gamete is larger, no differences have been detected in the dimensions of components such as microtubules and flagella.

Microtubules scattered in the cytoplasm of the young spermatocytes follow an irregular course and show no particular relationship to the blepharoplast, even during the differentiation of its periphery into basal bodies with characteristic triplets. Subsequently short lengths of notably straighter microtubules appear in quantity adjacent to the osmiophilic material lying along the microtubular ribbon of the developing gamete. These microtubules are particularly frequent around the distal ends of flagella beginning to develop from basal bodies, and often appear to converge upon them.

The view is put forward that the osmiophilic material adjacent to the microtubular ribbon, ontogenetically continuous with that originally at the centre of the differentiating blepharoplast, is responsible for the organization of the flagella. This material remains close to the ribbon throughout the differentiation of the gamete. If contact between the osmiophilic material and the flagella remains essential throughout their development, it would follow that they complete most or all of their growth parallel to the microtubular ribbon, possibly becoming emergent structures only as differentiation of the gamete is completed.

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