SUMMARY: Fine structure studies have shown that in oosphere development the protoplast of the oogonium of is cleaved by the formation of large vesicles which extend from the centre to join the plasmalemma. The origin and behaviour of the central vesicles is indicated by the presence in them of special granules which are identical with those in smaller cyto-plasmic vesicles and in the space formed in the oogonium at cleavage. The cytoplasmic vesicles also contain dense (osmiophilic) bodies, mostly about 0.3 μm in diameter, and in some fixations show proliferation of membranes. The contents of the vesicles often show lamellation as do those in vesicles in zoosporangia of where cytoplasmic cleavage occurs in the same way. The appearance of this material in sporangia coincides with an increase in the quantity of phosphatidyl choline.

The vesicles in germinating zoospores of are also produced by fusion of dense-body vesicles.

The presence of vesicles of the dense-body type in many Oomycetes and other micro-organisms is recorded and their functions are discussed.


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