Little is known of the biochemistry of diatoms, although many workers have reported growth experiments with the unicellular algae of the marine phyto-plankton. Experiments have often been performed without due regard for the appropriate control of physical and chemical conditions. Many reports contain only incomplete data of the growth under a given set of conditions, and it is often impossible to say whether the effects recorded are upon the growth rate, the total crop, or both. Other studies have been reported which included the addition of organic matter to cultures which were only uni-algal and not bacteria-free. At the present time even the mere maintenance of stock cultures of the marine unicellular algae is perforce an empirical matter. Results in replicate cultures often show gross differences in growth that are apparent on inspection by eye alone, and insufficient information is available regarding the nature of these variations in growth to allow the rational development of improved culture media. Due therefore to a lack of suitable techniques, most of the results available are difficult, if not impossible, to interpret in terms of the biochemical activities of the algae.