to the Plant Cell . 
513 
3. Advantages of certain formulae for nutrient solutions. 
In the first experiments upon algae and fern prothalli, I used the well- 
known formula of Knop in making the nutrient solution: — 
Calcium nitrate 4 g. 
Potassium nitrate 1 g. 
Magnesium sulphate . . . . . . 1 g. 
Potassium dihydrogen phosphate . . . . ig. 
Ferric chloride ....... trace. 
Distilled water ....... 7 litres. 
Repeated trials of this solution agreed in showing that it is unsuited for 
the growth of algae. A large quantity of nitrate is supplied in the form of 
calcium nitrate. The algae use the nitrate more rapidly than the calcium. 
As a result, the solution continually increases in alkalinity, and thereby 
becomes less and less suitable for the growth of Algae. A neutral or 
slightly acid medium is more favourable for the development of most 
algae, and this condition was fulfilled in the original solution by the 
presence . of the potassium dihydrogen phosphate. Unfortunately this 
condition is not maintained after the plants begin to grow, because the 
nitrate is removed from calcium nitrate, resulting in alkalinity due to 
calcium carbonate formed with the carbon dioxide always present in such 
cultures. The lower algae will thrive, as Molisch (’ 96 ) stated, in a slightly 
acid medium, and it is probable that the higher algae grow best when the 
solution is near the neutral point. Klebs (’ 96 ) found that a distinctly 
alkaline culture solution was necessary for the formation of zoospores in 
Vaucheria. The conditions favouring vegetative growth were not determined 
with respect to acidity. 
After discarding Knop’s formula, I employed the following modification 
of a formula of Beijerinck given by Moore (’ 03 ): — 
Ammonium nitrate 0-5 g. 
Potassium dihydrogen phosphate . . . . o *3 g. 
Magnesium sulphate 02 g. 
Calcium chloride 01 g. 
Ferric chloride ....... trace. 
Distilled water ....... 1,000 cc. 
The nutrient solution when made according to this formula, has a con- 
centration of 1,000 parts per million (o-i per cent.). This concentration is 
greater than necessary, in fact is much greater than that to which most 
plants are accustomed in nature. Though a more dilute solution would 
undoubtedly serve just as well, I have not made any attempts to determine 
the limits of concentration for optimum growth. 
This formula proved to be eminently satisfactory for the growth of 
