All stock solutions are to be preserved, tightly stoppered, in 

 darkness. The nutrient solutions to be actually employed in the 

 cultures are to be prepared, with proper dilution, from these 

 mixed stock solutions. The nutrient solutions may, of course, 

 have any calculated osmostic value below that of the mixed stock 

 solution. It is planned to begin the work using calculated osmotic 

 values of 1.0 atm. for all solutions and the data of tables I-VI all 

 refer to this value. The nutrient solutions themselves may be 

 preserved, tightly stoppered, in darkness (to prevent algal 

 growth, etc.), but it is undesirable to keep them too long, since 

 alterations might possibly occur. It seems safe to preserve 

 them as long as five or six weeks, but a more frequent prepara- 

 tion of new ones is probably desirable. There seems to be no 

 doubt that the stronger mixed stock solutions (types I-IV) 

 will keep indefinitely in darkness, as will also the single-salt 

 stock solutions. If solutions are preserved for very long periods 

 the solubility of the glass of the containers may become a consid- 

 erable feature. If the bottles are internally paraffined this pos- 

 sibility is largely removed. 



Supplementary Tables. Tables VII-XII give the amounts of 

 water and of each of the requisite single-salt stock solutions that 

 are needed to make a liter of each of the most concentrated 

 nutrient solutions for each of the six different solution types. 

 For example, solution IRISI (table VII) is made by placing 

 924.7 cc. of water in a suitable container and then adding to it, 

 with shaking, first 9.45 cc. of molecular KH^POs then 9.45 cc. 

 of molecular Ca(N03)^ and finally 56.4 cc. of molecular MgSO^ 

 Of course every single-salt stock solution is always employed 

 with the concentration shown in parentheses below the formula 

 for that salt in these tables. (See page 36 of this Plan.) The 

 stock nutrient solutions of types V and VI have an osmotic value 

 of 1.0 atmosphere, while those of types I-IV are more concen- 

 trated. The solutions of types V and VI cannot be generally 

 made with higher concentrations than this value of 1.00 atm. 

 From tables VII-X and from page 36 it is clear that the stock 

 nutrient solutions of types I and III are planned to be made 3.5 

 times — and those of types II and IV 3.0 times — as concentrated 

 as will be needed for solutions having an osmotic value of 1.00 

 atmosphere. Of course other procedures may be followed in 

 making the nutrient solutions actually used, but this plan sup- 

 poses that the stock nutrient solutions will be prepared as here 

 set forth, using the factor 1.0 for types V and VI, 3.5 for types 

 I and III, and 3.0 for types II and IV. (See p. 37 of this Plan.) 



Solutions VR1S6, VIR1S8, and VIR2S5 are not possible with 

 an osmotic value of 1.00 atm.; they cannot be tested except in 

 series having a lower total concentration than this. 



38 



