early growth of wheat, the solution called control in the preced- 

 ing pages. It is largely through these controls that climatic 

 conditions and different groups of solutions tested at different 

 times and places are to be compared. At a later time it may be- 

 come expedient to adopt some other solution as general control, 

 but the one mentioned is the logical one to use in the early stages 

 of our studies. 



The following paragraphs aim to present some of the most 

 promising ways of grouping the one hundred and twenty-three 

 solutions that are first to be tested (osmotic value, 1.00 atm.). 



Suhdivision by Types. Each set of 21 (or 19 or 20) solu- 

 tions (tables I-VI) furnishes a logical group for experimen- 

 tation. Such a group includes (with the triplicate control) 22, 

 23 or 24 cultures, which is a convenient number for an experi- 

 menter who does not devote nearly all his time to the work. It 

 may be noted that types V and VI involve some physical-chemical 

 difficulties not encountered with the others, and those who have 

 had experience with this sort of difficulty are urged to undertake 

 the study of these two exceptional types. Type I is the one on 

 which most of the earlier work has been done. 



Of course it will be desirable, where possible, to carry out 

 each experiment with these type groups in duplicate, triplicate, 

 etc., and an experimenter may thus give his entire time to the 

 solutions of a single group. 



It will also be desirable, especially where two or more experi- 

 menters can work together, that the full sets of several solution 

 types (or even all six of them) be tested simultaneously, in which 

 case a single triplicate control will serve for all sets. 



Suhdivision Into Groups Smaller Than Type Groups. For 

 smaller groups than are represented by the six different types of 

 solution, any solutions may be selected, either merely at random, 

 or because of a personal interest. It will be especially desirable 

 to study and compare in this way just those solutions that have 

 already given good promise. For the seedling phase of growth 

 Shive's (1915) results and those of Livingston and Tottingham 

 (1918) are of special interest as indicating promising solutions. 

 A study of Shive's graphic summary (page 390) for his optimal 

 concentration will suggest small groups of solutions of type I 

 that may be profitably compared. Table 2 of Livingston and 

 Tottingham may furnish similar suggestions for type III. Many 

 other sources of similar suggestions will doubtless become avail- 

 able as soon as a few experiments has been carried out, and such 



51 



