A large variety of culture media has been described for the growth of photosynthetic microorganisms in the laboratory. Exact data on growth rates, however, are relatively scarce. Moreover, papers containing such information do not always reveal this by their title.
Since it appeared desirable to obtain quantitative information about growth characteristics of algal strains used in our laboratory, we determined growth rates of our organisms under various conditions and, when possible, compared our results with data given by other authors.
This paper also includes a survey of growth rates of photosynthetic microorganisms reported in the literature. As far as we know no such summary has been published since MY~I~S' review (1953).
Culture technique
The organisms used in our experiments were cultured in glass vessels closely resembling those described by Koc~ (1953) except that they were closed by means of aluminium caps, and that the side tubes for gas supply constituted fixed parts of the vessels instead of being attached by rubber tubings. The diameter of the main compartment was about 35 ram, its height 31 era. Usually the vessels contained about 150 ml of liquid culture medium. Up to seven of the vessels were placed in thermostated perspex water baths filled with distilled water. The temperature in the vessels was constant within ~= 0.3~ The baths were placed in wooden boxes, painted white inside, and equipped with tubings for supply of gas and of cooling water. The water baths remained free of algal growth, perhaps because of an inhibitory effect of the copper cooling tubings or because algae are unable to adhere to the perspex surface. The culture vessels were fixed to the rear wall of the boxes by means of clips. The whole set-up is shown in Fig. 1.
The culture vessels were illuminated by banks of 1--5 Philips TL 20W/32 "warm-white" fluorescent tubes. These banks could be replaced by tungsten lamps if desired. Unless otherwise stated the algae were gassed with a mixture of dry air and 4.5--5.50/0 C02. It was found that evaporation was negligible below 40~ at higher temperatures a small correction was made. Cotton plugs in the upper parts of the inlet tubes intercepted contaminations. The flow rate of the gas mixture usually was 15--30 ml/min and could be regulated for each vessel separately by means of a needle valve. For some organisms (Porphyridium, Navicula) it was neces-