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THE AMEBIC AN NATURALIST [Vol. XL VII 



the existence of a selective mortality, one must work 

 with as large numbers of seeds as possible in order to 

 obtain a reliable measure of selective mortality as well 

 as decisive constants for the relationship between seed 

 weight and time required for germination, if it be of the 

 low or moderate order that one might expect. It is 

 desirable that the germination tests be made under con- 

 ditions as uniform as possible. The technique adopted 

 must also be practical— that is, in the case of the present 

 study, the work- was necessarily done at a season of the 

 year when it would not interfere with other experiments ; 

 the seeds had to be germinated so that each of the many 

 hundreds or thousands of pots could be examined without 

 too great back or eye strain every three hours through- 

 out the twenty-four during the whole period of germina- 

 tion ; finally, the expense of setting up and maintaining 

 the experiment had to be kept within reasonable limits. 



These requirements seemed, after careful considera- 

 tion, best met by planting the seeds separately in three- 

 inch pots of moderately fine sand. To facilitate hand- 

 ling, the pots were filled with slightly moist sand which 

 was generally allowed to dry before the seeds were 

 planted. The whole experiment was then watered at the 

 same time. In a few instances, it was impossible to have 

 the sand of all the pots perfectly dry when the seeds 

 were planted, but I believe this introduces only a small 

 source of error, for in these cases the planting was rushed 

 through as rapidly as possible, and the individually 

 labeled seeds were always thoroughly shuffled before 

 planting to counteract, in as far as might be, the hetero- 

 geneity of environmental conditions afforded by different 

 parts of the greenhouse. The space on the benches was 

 filled to the level of the top of the pots with sand to 

 prevent too great evaporation. The labels were com- 



