Note on the technique of making bacteria-free cultures of marine diatoms

There is a great demand for algal cultures in studying morphology, cytology, ecology, cellular pathology and physiology, identification of species, and biotic interaction, and also in feeding small animals in culture for various studies. It is hoped that the following note may be of some use to those who want to start making pure cultures of marine phytoplankton organisms.

Quantitative evolution; the diatoms

A Summary of the facts with numerical details omitted can be given as follows. In the diatoms—

1. Species-lifetimes have been alternatively short or long.

2. The main ratios of shorts to longs, or evanescents to permanents, e/p, are 3:1 for Centrales, 10:6 for Fragilariaceæ, 7:9 for allogamous Pennales. These ratios or nearest approaches to these ratios occur in the above three groups, (a) in each group as a whole; (b) in species-arising in each group per geological subperiod; and (c) in heterogeneous genera in each genus as a whole and in each genus per subperiod. A derivative 1:3 ratio also occurs in some pennate genera. There are some significant and understandable exceptions.