Scale bars indicate 20 µm (1), 5 µm (2, 3), 1 µm (4).

Four images in a slide changer.
Please click on < or > on the image edges or on the dots at the bottom edge of the images to browse through the slides!

The magnification series above impressively shows the network of cellulose microfibrils in the primary wall. The protuberances, marked with arrows, represent the pore apparatuses in the underlying secondary wall.

In the last image, at the highest magnification, the diameters of the microfibrils become measurable. Within the limits of measurement accuracy, the finest visible strands have diameters of approximately 10 nm. This order of magnitude corresponds well with the findings of Giddings et al. (1980). They had observed that during the formation of the primary wall, isolated production apparatuses of cellulose microfibrils (so-called rosettes) produce microfibrils with a diameter of 5 nm. They were further able to show that during the formation of the secondary wall, hexagonally arranged arrays of rosettes produce complex fibrils with a diameter of 28 nm, which form the basis of the secondary wall.

References

Brook, A. J. (1981). The biology of desmids (Vol. 16). University of California Press.

Giddings Jr, TH, Brower, DL, & Staehelin, LA (1980). Visualization of particle complexes in the plasma membrane of Micrasterias denticulata associated with the formation of cellulose fibrils in primary and secondary cell walls. The Journal of cell biology , 84 (2), 327-339.