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 : 



