[Vor. 1 
24 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
phases of nutrition. With the development of a clearer under- 
standing of the activities and life processes of the various 
micro-organisms, the necessity of working with rigorously 
pure cultures has become more and more evident. It is now 
generally appreciated that, in most cases, valid conclusions as to 
the physiology of a particular organism cannot be drawn with 
certainty where one or more foreign organisms have been present 
in the cultures. There can be no doubt that the frequent con- 
tamination of cultures of alge with bacteria, and even with 
fungi, has, in many cases, detracted markedly from the value 
of painstaking and otherwise careful physiological investigations. 
The readiness, however, with which many alge lend themselves 
to experimental purposes—on account of their small size and 
ease of handling and culture—will always make them favored 
objects of study; and it appears desirable at this time to bring 
together some of the experiences of the author in the prepara- 
tion of pure cultures of alge, with the hope that suggestions 
may be gained from them by those who desire to obtain such 
eultures for one purpose or another. 
An unfortunate use of the term “риге culture" has come 
into more or less general use and has frequently led to confusion 
and ambiguity. Ав used by many authors, it means simply 
a culture of a single species of alga not necessarily free from 
bacteria and fungi. Where the presence of other organisms 
is not specifically mentioned, it is clear that the above usage 
of the term may lead to serious misunderstandings. Indeed, 
it remains for the reader, in many instances, to decide for 
himself—from the technique employed—whether a culture of 
an alga free from all other organisms or only from other species 
of alge is meant. It is to be hoped, therefore, that the term 
pure culture shall come to have the same clearly defined mean- 
ing when used in connection with the alge that it has long had 
in the fungi and bacteria. In the following report the term 
is used to signify a culture of a single species of alga free from 
all other organisms. 
HISTORICAL 
Although incidental references to pure culture technique in the 
algæ are frequently found in the literature, relatively few con- 
tributions have appeared which deal extensively with the 
