Some aspects of the origin of diatoms and their subsequent evolution.

This paper briefly explores the idea that morphological variation in diatoms was and is restricted during the formation of new siliceous elements at each cell division by the constraints imposed by enclosure in a non-malleable "tube" of silica against which the protoplast is maintained by internal pressure. This allows little scope for variation and thus diatoms from a very early geological period have retained basic morphological forms which arose during the original burst of evolution when the siliceous elements were in some way more plastic. The radiation of distinctive basic morphological forms into the plankton, epiphyton and epipelon is also touched upon.