Winifred E. Brenciilev 



229 



B. Nutrient Solutions never changed. 



l.y^ period of growth. 



The series in which the solutions were never cliauged were set up to 

 correspond in time as closely as possible with those in which the food 

 was renewed. The following table shows how exactly the two sets 

 correspond with regard to the length of the first period of growth. 



The only instance in which the first period varied by even a week was 

 when there was five days difference in the date of beginning the experi- 

 ment. At that time of year, in September, both temperature and sunlight 

 were falling and the difference of nearly a week would fully account for 

 the prolongation of the first period of growth in the later started plants. 

 This series is therefore left out of consideration in drawing up com- 

 parisons. The close correspondence shows that during the first period of 

 the plant's development under the experimental conditions the presence 

 of an excess of nutrients, below toxic limits, has no effect upon growth. 

 Very little mineral matter is sufficient to supply the needs of the seedling 

 and the fresh quantity given when the solutions are changed is disregarded 

 and exercises neither a beneficial nor harmful action. As a matter of fact, 

 so little food salt is withdrawn from the solution at this time that the 

 fresh solution added weekly closely resembles the old, and it is probable 

 that no difference is detected by the plant. 



2nd period of growth. 



As the series with changed and unchanged food solutions were 

 carried on together the conditions of sunlight and temperature were 

 identical in each case, the only different factor being that in one set an 

 unlimited supply of food was available and in the other a very limited 

 quantity was at the disposal of the plants. 



16—2 



