242 THE MAINTENANCE OF THE INDIVIDUAL 



have been experimenting and are still experimenting in the attempt 

 to solve the problem. 



With this background, our point of view is to consider the living 

 green plant as an organism, faced by the same kinds of problems as a 

 living animal, taking a living from its environment, storing up food 

 for the inevitable time of food shortage, and eventually forming 

 fruits to hold the seeds which are necessary to pass the stream of life 

 on to the next generation. Unlike an animal, the green plant takes 

 raw food materials from its environment and, under certain favorable 

 conditions, synthesizes them into organic foods, a process effected 

 by means of a number of adaptive structures, in certain, favorable 

 environmental conditions, the chief of which is sunlight. 



By burning the body of a hving plant until nothing but ash remains, 

 and then making a careful analysis of this residue, frequently as many 

 as thirty chemical elements are found. Twelve are nearly always 

 present, eight of which are essential to plant growth. The latter are 

 boron, calcium, iron, magnesium, manganese, phosphorus, potassium, 

 and sulphur. It will be noticed that this list does not agree exactly 

 with the previous list of elements usually found in the protoplasm of 

 Hving things (page 131), but the implication is clear. The chemical 

 elements found in living matter, as previously noted, are also found 

 in rocks or soil, air, and water. The stage is set and it remains for 

 the scientist to discover just how these elements, found in the environ- 

 ment, can be made into food and living stuff by the green plant. 



A good many experiments have been made with plants to determine 

 more exactly the function of these elements. It has been shown 

 that if green plants are placed in a nutrient solution containing the 

 necessary elements,^ growth will take place. If, however, certain 

 elements are subtracted from the solution, the plants will not develop, 

 or their growth will be considerably slowed down. Such experiments 

 give us our first clue to one important use of the root. It is evidently 

 an absorbing organ through which the plant takes in not only water, 

 but some of the essential mineral materials necessary for its growth. 



1 A list of the most commonly used nutrient solutions for plant growth are given below. 



Crone's solution : Water, 2.0 1. ; KNO3, 1.0 g. ; FeP04, 0.5 g. ; CaS04, 0.25 g. ; MgSOj, 0.25 g. 



Detmer's solution: Water, 1000 g. ; Ca(N03)2, 1.0 g.; KCl, 0.25 g. ; MgS04, 0.25 g. ; KH2PO4, 

 0.25 g. ; FeClj, trace. 



Knop's solution: Water, 1000 g. ; Ca(N03)2, 1.0 g. ; KNO3, 0.25 g. ; KH2PO4, 0.25 g. ; MgS04, 

 0.25 g. ; FeP04, trace. 



Pfeffer's solution : Water, 3-7 1. ; Ca(N03)2, 4 g. ; KNO3, 1 g. ; MgS04, 1 g. ; KH2PO4, 1 g. ; KCl, 

 0.5 g. ; FeCls, trace. 



Sach's solution : Water, 1000 g. ; KNO3, 1.00 g. ; NaCl, 0.50 g. ; CaS04, 0.50 g. ; MgS04, 0.50 g. ; 

 Ca3(P04)2, 0.50 g. ; FeCls, 0.005 g. 



