Mineral Nutrients 165 



Again, such plants as corn and vigorous varieties of the 

 sunflower are able to force the roots through the paraffin, 

 especially in warm weather. 



LABORATORY WORK. SUGGESTED EXPERIMENTS 



Solution cultures, essential nutrients. Since the seed repre- 

 sents a considerable accumulation of the necessary food-materials 

 required by the growing plant, the absolute necessity of a particu- 

 lar nutrient may not be readily demonstrated except by growing 

 plants to maturity in relatively large vessels. The latter is com- 

 monly impracticable, and in simple experiments it suffices to 

 determine the comparative effects upon growth or green weight 

 of a full nutrient solution, along with other solutions lacking 

 each element in turn. While the method is open to criticism, 

 the student will find much use for the experience in manipulation ; 

 and after a study of balanced solutions, he may define his criti- 

 cism. 



Materials needed : cheap tumblers covered and arranged as 

 suggested (section 77 and figure 44), or wide-mouth bottles with 

 flat corks notched to receive the seed ; black paper shells for 

 darkening the cultures, and black paper circles or squares dipped 

 in hot paraffin for tumbler covers ; chemicals required by the so- 

 lution ; as many stock flasks, or bottles, as nutrients ; distilled 

 water, graduates, rubber bands and labels ; and germinating 

 seed. 



Uniform seedlings should be employed, and these should be 

 grown on moist moss or sawdust, or upon a paraffined wire screen 

 floated on water by corks, but sufficiently weighted to keep the 

 seed moist. All vessels should be chemically clean (preferably 

 by the acid-dichromate method), and only the purest chemicals 

 and distilled water employed. 



Prepare a stock solution of each main constituent of the Pfeffer 

 solution in the proportional quantity of water, thus for a 5000 cc. 

 solution, as follows : 



