1. Frey-Wyssling, A., “Submicroscopic Morphology of Protoplasm, and its Derivatives” (Elsevier, New York, 1948).
2. Preston, R. D., Proc. Roy. Soc., B, 134, 202 (1947).
3. Castle, E. S., J. Cell. Comp. Physiol., 10, 113 (1937).
4. Iterson, G. van, Protoplasma, 27, 190 (1937).
5. Cruger, H. (1855), not seen; see Sinnot, E. W., and Bloch, R. Amer. J. Bot., 32, (3), 151 (1945).